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  • 1. Al-Zoubi, Noura
    et al.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Uppsala University, Uppsala, Sweden .
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Uppsala University, Uppsala, Sweden; Wigner Research Center for Physics, Budapest, Hungary .
    Influence of manganese on the bulk properties of Fe-Cr-Mn alloys: a first-principles study2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, no 12, p. 125702-Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of manganese on lattice stability and magnetic moments of paramagnetic Fe-Cr-Mn steel alloys along the Bain path connecting the body-centered cubic (bcc) and face-centered cubic (fcc) structures. The calculations are carried out using the ab initio exact muffin-tin orbital method, in combination with the coherent potential approximation, and the paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all Fe-Cr-Mn alloys considered here, the local magnetic moments on Fe atoms have the minimum values for the fcc structure and the maximum values for the bcc structure, whereas the local magnetic moments on Mn have almost the same value along the constant-volume Bain path. Our results show that Mn addition to paramagnetic Fe-Cr solid solution stabilizes the bcc structure. However, when considering the paramagnetic fcc phase relative to the ferromagnetic bcc ground state, then Mn turns out to be a clear fcc stabilizer, in line with observations.

  • 2.
    Al-Zoubi, Noura
    et al.
    Tafila Tech Univ, Dept Appl Phys, Tafila, Jordan..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic properties of 4d transition metal alloys: Values and trends2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 159, p. 273-280Article in journal (Refereed)
    Abstract [en]

    Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEso1), we study the single crystal elastic constants of 4d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z(Z + 1) and between the second neighbors Z(Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C-fcc'-2C(bcc)' and the structural energy difference between the fcc and bcc lattices Delta E is superior to the previously considered models. For a given crystal structure, the equiatomic Z(Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z(1-x)(Z + 2)(x) possess similar properties as Z(1-2x)(Z + 1)(2x). The present theoretical data on the structural and the elastic properties of 4d transition metal alloys provides consistent input for coarse scale modeling of material properties.

  • 3.
    Cheng, Q.
    et al.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Xu, X. D.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China.;Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Y. P.
    Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    Nieh, T. G.
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Chen, M. W.
    Johns Hopkins Univ, Dept Mat Sci & Engn, Baltimore, MD 21214 USA..
    Solid solution softening in a Aloi CoCrFeMnNi high-entropy alloy2020In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 186, p. 63-68Article in journal (Refereed)
    Abstract [en]

    Solute effects on high-entropy alloys of equiatomic proportions are scientifically intriguing because there is no such well-defined "solute" and "solvent" atoms compared to those of conventional single principal element alloys. To date, most of the face-centered cubic alloys exhibit solid solution strengthening rather than softening due to the interactions between dislocations and solute atoms. Here, we present the careful experimental measurements and demonstrate solid solution softening, albeit weak, in a single phase CoCrFeMnNi through the minor addition of 2. at.% Al. This softening effect is mostly related to the decreased Peierl's stress by Al addition.

  • 4.
    Cheng, Q.
    et al.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Xu, X. D.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Xie, P.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Han, L. L.
    Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    He, J. Y.
    Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Zhang, J.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Li, Z. T.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Li, Y. P.
    Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    Liu, B.
    Cent South Univ, State Key Lab Powder Met, Changsha 410083, Peoples R China..
    Nieh, T. G.
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Chen, M. W.
    Johns Hopkins Univ, Dept Mat Sci & Engn, Baltimore, MD 21214 USA..
    Chen, J. H.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Unveiling anneal hardening in dilute Al-doped AlxCoCrFeMnNi (x=0, 0.1) high-entropy alloys2021In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 91, p. 270-277Article in journal (Refereed)
    Abstract [en]

    Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic (FCC) structure, whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature (T-rx). Microscopically, this hardening effect has been ascribed to several mechanisms, i.e. solute segregation to defects (dislocation and stacking fault) and short-range chemical ordering, etc. However, none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys (HEAs). Here we report the observations, using high-resolution electron channeling contrast imaging and transmission electron microscopy, of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi HEA subject to an annealing below T-rx. The dislocation substructures are observed to be thermally stable up to T-rx, which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation occurs. The microstructure feature is markedly different from that of conventional dilute solid solution alloys, in which dislocation substructures gradually vanish by recovery during annealing, leading to a strength drop. Furthermore, dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed (<= 500 degrees C) HEA. This Al induced softening effect, could be associated with the anisotropic formation of dislocation substructure, resulting from enhanced dislocation planar slip due to glide plane softening effect. These findings suggest that the strength of HEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.

  • 5.
    Cheng, Qing
    et al.
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    Mo, Jinyong
    China Univ Min & Technol, Inst Mass Amorphous Met Sci, Sch Mat Sci & Phys, Xuzhou 221116, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Xu, Xiandong
    Hunan Univ, Coll Mat Sci & Engn, Ctr High Resolut Electron Microscopy, Changsha 410082, Peoples R China..
    A revisit to the role of Mo in an MP35N superalloy: An experimental and theoretical study2023In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 157, p. 60-70Article in journal (Refereed)
    Abstract [en]

    Molybdenum (Mo) has been recognized as an essential alloying element of the MP35N (Co35.4Cr22.9Ni35.5Mo6.2, at.%) superalloy for enhancing strength and corrosion resistance. However, a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking. In this work, we consider five (Co37.7Cr24.4Ni37.9)100-xMox (x = 0, 0.7, 2.0, 3.2, and 6.2) alloys, and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged. It is found that strong solid solution strengthening (SSS) is a main domain to the improved yield strength, whereas grain boundaries are found to soften by the Mo addition. The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS, and the grain boundary softening effect is mostly associated with the decreased shear modulus. Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy (SFE) reduces by the Mo addition. The calculated SFE value decreases from 0.4 mJ/m2 to-11.8 mJ/m2 at 0 K as Mo content increases from 0 at.% to 6.2 at.%, and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m2 and 9 mJ/m2, respectively. The reduction of SFE promoted the generation of stacking faults and deformation twins, which sustain a high strain hardening rate, thus postponing necking instability and enhancing tensile strength and elongation.

  • 6.
    Hu, Jutao
    et al.
    School of Physics, University of Electronic Science and Technology of China, Chengdu, 611731, China.
    Wang, Weidu
    Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China; Institute of Modern Physics, Fudan University, Shanghai 200433, China.
    Xie, Lei
    Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China.
    Sun, Guangai
    Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China.
    Shen, Huahai
    Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Pengcheng
    School of Physics, University of Electronic Science and Technology of China, Chengdu, 611731, China.
    Zhang, Jianwei
    School of Physics, University of Electronic Science and Technology of China, Chengdu, 611731, China.
    Zu, Xiaotao
    School of Physics, University of Electronic Science and Technology of China, Chengdu, 611731, China.
    Xiao, Haiyan
    School of Physics, University of Electronic Science and Technology of China, Chengdu, 611731, China.
    Effects of NH4+ doping on the hydrogen storage properties of metal hydrides2023In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 48, no 50, p. 19153-19159Article in journal (Refereed)
    Abstract [en]

    Doping can modify the properties of metal hydrogen storage materials significantly. Currently, the metal doping is a frequent strategy, while the non-metal cation doping has not been examined extensively so far. In this study, the effects of NH4+ doping on the hydrogen storage properties of different metal hydrides, including TiH2, Ti0·25V0·25Nb0·25Zr0·25H2, Ti0·5V0·5H2 and VH2, are investigated by first-principles calculations. It is found that the NH4+ presents a good affinity for metal hydrides and the NH4+ incorporation leads to charge redistribution and formation of dihydrogen bond. Furthermore, the NH4+ doping in metal hydrides is favorable for enhancing the hydrogen storage capacity and decreasing the thermal stability simultaneously. The possible reason for the NH4+ doping induced destabilization in metal hydrides is the relatively weak interaction between NH4+ and hydrogen atoms.

  • 7.
    Hu, Jutao
    et al.
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Zhang, Jinjing
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Li, Menglu
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Zhang, Sa
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Xiao, Haiyan
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Xie, Lei
    China Acad Engn Phys, Inst Nucl Phys & Chem, Mianyang 621900, Sichuan, Peoples R China..
    Sun, Guangai
    China Acad Engn Phys, Inst Nucl Phys & Chem, Mianyang 621900, Sichuan, Peoples R China..
    Shen, Huahai
    China Acad Engn Phys, Inst Nucl Phys & Chem, Mianyang 621900, Sichuan, Peoples R China..
    Zhou, Xiaosong
    China Acad Engn Phys, Inst Nucl Phys & Chem, Mianyang 621900, Sichuan, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Pengcheng
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Zhang, Jianwei
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Zu, Xiaotao
    Univ Elect Sci & Technol China, Sch Phys, Chengdu 611731, Peoples R China..
    The origin of anomalous hydrogen occupation in high entropy alloys2022In: Journal of Materials Chemistry A, ISSN 2050-7488, E-ISSN 2050-7496, Vol. 10, no 13, p. 7228-7237Article in journal (Refereed)
    Abstract [en]

    Metal hydrogen storage materials have been the focus of intensive research in the field of hydrogen-based economy. An outstanding question is that the number of hydrogen atoms accommodated in metal hydrides is generally much below the number of interstices, which limits their hydrogen storage capacities. Unlike traditional FCC metal hydrides where hydrogen can only occupy tetrahedral interstices, this study demonstrates that hydrogen can also occupy octahedral interstices in FCC high entropy alloy (HEA) hydrides, which leads to the violation of the Switendick criterion. For Ti25V25Nb25Ta25 and Ti25V25Nb25Zr25 HEAs, nearly 20% and 17.5% of octahedral interstices can be occupied by hydrogen, respectively. The anomalous hydrogen occupation mainly originates from the intrinsic electron delocalization between hydrogen atoms in HEA hydrides, which presents a sharp contrast to traditional metal hydrides. Such electron delocalization decreases repulsive interactions between hydrogens and promotes the electron localization at octahedral interstices. Additionally, this study reveals that hydrogen occupation at octahedral interstices enhances the structural disordering and decreases the thermal stability of HEA hydrides, which will be beneficial to reduce the dehydrogenation temperature. The presented results may provide a new strategy for the design of high-density storage materials.

  • 8.
    Huang, He
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Dong, Zhihua
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Huang, Shuo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Meng, Daqiao
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Lai, Xinchun
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Liu, Tianwei
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Zhu, Shengfa
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 149, p. 388-396Article in journal (Refereed)
    Abstract [en]

    The CrCoNi-based medium and high entropy alloys (MHEAs) have drawn much attention due to their exceptional mechanical properties at cryogenic temperatures. The twinning critical resolved shear stress (CRSS) is a fundamental parameter for evaluating the strength-ductility properties of MHEAs. Here we construct and apply an extended twinning nucleation Peierls-Nabarro (P-N) model to predict the twinning CRSSes of face-centered cubic (FCC) CrCoNi-based MHEAs. The order of the twinning CRSSes of the selected alloys is CrCoNi > CrCoNiMn > CrCoNiFe > CrCoNiFeMn and the values are 291, 277, 274 and 236 MPa, respectively. These theoretical predictions agree very well with the experimental twinning CRSSes of CrCoNi and CrCoNiFeMn accounting for 260 +/- 30 and 235 +/- 10 MPa, respectively and are perfectly consistent with the strength-ductility properties including yield stress, ultimate tensile stress and uniform elongation for fracture of the FCC CrCoNi-based MHEAs obtained at cryogenic temperatures. The present method offers a first-principle quantum-mechanical tool for optimizing and designing new MHEAs with exceptional mechanical properties. 

  • 9.
    Huang, He
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Sci & Technol Surface Phys & Chem Lab, Mianyang 621907, Sichuan, Peoples R China..
    Wang, Xin
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Shi, Jie
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621907, Sichuan, Peoples R China..
    Huang, Huogen
    Zhao, Yawen
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Xu, Haiyan
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Zhang, Pengguo
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Long, Zhong
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Bai, Bin
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Fa, Tao
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Ma, Ce
    Sci & Technol Surface Phys & Chem Lab, Mianyang 621907, Sichuan, Peoples R China..
    Li, Fangfang
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Meng, Daqiao
    China Acad Engn Phys, Inst Mat, Mianyang 621900, Sichuan, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Material informatics for uranium-bearing equiatomic disordered solid solution alloys2021In: Materials Today Communications, ISSN 2352-4928, Vol. 29, article id 102960Article in journal (Refereed)
    Abstract [en]

    Near-equiatomic, multi-component alloys with disordered solid solution phase (DSSP) are associated with outstanding performance in phase stability, mechanical properties and irradiation resistance, and may provide a feasible solution for developing novel uranium-based alloys with better fuel capacity. In this work, we build a machine learning (ML) model of disordered solid solution alloys (DSSAs) based on about 6000 known multicomponent alloys and several materials descriptors to efficiently predict the DSSAs formation ability. To fully optimize the ML model, we develop a multi-algorithm cross-verification approach in combination with the SHapley Additive exPlanations value (SHAP value). We find that the Delta S-C, Lambda, Phi(s), gamma and 1/Omega, corresponding to the former two Hume - Rothery (H - R) rules, are the most important materials descriptors affecting DSSAs formation ability. When the ML model is applied to the 375 uranium-bearing DSSAs, 190 of them are predicted to be the DSSAs never known before. 20 of these alloys were randomly synthesized and characterized. Our predictions are in-line with experiments with 3 inconsistent cases, suggesting that our strategy offers a fast and accurate way to predict novel multi-component alloys with high DSSAs formation ability. These findings shed considerable light on the mapping between the material descriptors and DSSAs formation ability.

  • 10.
    Huang, Shuo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Huang, He
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, 621900, PR China.
    Li, Wei
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, SE-75120, Uppsala, Sweden.
    Kim, Dongyoo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Department of Physics, Pukyung National University, Busan, 608-737, Republic of Korea.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Holmström, E.
    Kwon, S. K.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Twinning in metastable high-entropy alloys2018In: Nature Communications, E-ISSN 2041-1723, Vol. 9, no 1, article id 2381Article in journal (Refereed)
    Abstract [en]

    Twinning is a fundamental mechanism behind the simultaneous increase of strength and ductility in medium- and high-entropy alloys, but its operation is not yet well understood, which limits their exploitation. Since many high-entropy alloys showing outstanding mechanical properties are actually thermodynamically unstable at ambient and cryogenic conditions, the observed twinning challenges the existing phenomenological and theoretical plasticity models. Here, we adopt a transparent approach based on effective energy barriers in combination with first-principle calculations to shed light on the origin of twinning in high-entropy alloys. We demonstrate that twinning can be the primary deformation mode in metastable face-centered cubic alloys with a fraction that surpasses the previously established upper limit. The present advance in plasticity of metals opens opportunities for tailoring the mechanical response in engineering materials by optimizing metastable twinning in high-entropy alloys. 

  • 11.
    Huang, Shuo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Holmström, E.
    Varga, L. K.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Wigner Research Centre for Physics, Hungary; Uppsala University, Sweden.
    Mechanism of magnetic transition in FeCrCoNi-based high entropy alloys2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, p. 71-74Article in journal (Refereed)
    Abstract [en]

    First-principles alloy theory and Monte-Carlo simulations are performed to investigate the magnetic properties of FeCrCoNiAlx high entropy alloys. Results show that face-centered-cubic (fcc) and body-centered-cubic (bcc) structures possess significantly different magnetic behaviors uncovering that the alloy's Curie temperature is controlled by the stability of the Al-induced single phase or fcc-bcc dual-phase. We show that the appearance of the bcc phase with increasing Al content brings about the observed transition from the paramagnetic state for FeCrCoNi to the ferromagnetic state for FeCrCoNiAl at room-temperature. Similar mechanism is predicted to give rise to room-temperature ferromagnetism in FeCrCoNiGa high entropy alloy.

  • 12.
    Huang, Shuo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Huang, He
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle2018In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 210, p. 37-42Article in journal (Refereed)
    Abstract [en]

    The elastic parameters and ideal tensile strength in the 10011 direction for the body-centered cubic solid solution phase of FeCrCoMnAlx (0.6 <= x <= 1.5) high-entropy alloys are determined using first-principle alloy theory. Based on the estimated theoretical Curie temperatures, all alloys considered here are predicted to order ferromagnetically at room temperature. The mechanical behaviors are analyzed through the single-crystal and polycrystalline elastic moduli, Pugh ratio, and Debye temperature by making use of a series of phenomenological models. High ideal tensile strength is found for the equiatomic FeCrCoMnAl system, and the intrinsic strength increases with decreasing Al content.

  • 13.
    Li, Guijiang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delczeg-Czirjak, Erna K.
    Kvashnin, Yaroslav O.
    Eriksson, Olle
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 26, p. 262405-Article in journal (Refereed)
    Abstract [en]

    The magnetic state of the FeMnP0.75Si0.25 alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP0.75Si0.25 with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP0.75Si0.25 sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials.

  • 14. Li, R.
    et al.
    Zhang, P.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, C.
    Zhao, J.
    First-principles study of the behavior of O, N and C impurities in vanadium solids2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 435, no 1-3, p. 71-76Article in journal (Refereed)
    Abstract [en]

    Vanadium alloys are promising candidate for the structural materials of first-wall in future fusion reactor. In realistic vanadium alloys, there always exist some impurities (e.g. oxygen, nitrogen and carbon). To understand the microscopic behavior of these impurities, we investigated energetic and diffusion of O, N and C impurities as well as O-O/N-N/C-C interactions in pure vanadium using first-principles calculations. The O, N and C atoms prefer to occupy an octahedral interstitial site, and exhibit high diffusion barrier with 1.23 eV, 1.48 eV and 1.14 eV via diffusing between two neighboring octahedral interstitial sites, respectively. Such high barriers indicate that these impurities are hard to diffuse inside bulk vanadium. The corresponding diffusion coefficients as function of temperature were estimated using the Arrhenius diffusion equation. Our theoretical results provide the fundamental parameters for understanding the impurity effects in early stage of irradiation damage.

  • 15.
    Li, Xiaojie
    et al.
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China.;KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Ruihuan
    Changzhou Vocat Inst Mechatron Technol, Inst Mold Technol, Changzhou 213164, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Understanding the mechanical properties of reduced activation steels2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 146, p. 260-272Article in journal (Refereed)
    Abstract [en]

    Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic alpha-Fe and Fe91Cr9, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe91Cr9. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe91Cr9 is shown to provide an excellent approximation for the ab initio values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle.

  • 16.
    Li, Xiaojie
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Dalian University of Technology, China.
    Schonecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Ruihuan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Wang, Yuanyuan
    Zhao, Jijun
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Department of Physics and Astronomy, Division of Materials Theory, Sweden.
    Vitos, Levente
    Department of Physics and Astronomy, Division of Materials Theory, Sweden; Wigner Research Center for Physics, Hungary.
    Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 29, article id 295501Article in journal (Refereed)
    Abstract [en]

    To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0 <= x, y <= 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young's modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C-11, the other elastic parameters including C-12, C-44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-yOsy than in W1-xRex. A strong correlation between C' and the fcc-bcc structural energy difference for W1-x-yRexOsy is revealed demonstrating that canonical band structure dictates the alloying effect on C'. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.

  • 17.
    Li, Xiaojie
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hao, Shengzhi
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Zhao, Jijun
    Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China..
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys2019In: Physical Review Materials, E-ISSN 2475-9953, Vol. 3, no 3, article id 034401Article in journal (Refereed)
    Abstract [en]

    A density-functional theory investigation of the (100) and (110) surfaces of the body-centered cubic (bcc) Fe1-xbCrxb binary alloys, x(b) <= 15 at.%, is reported. The energies and segregation energies of these surfaces were calculated for chemically homogeneous concentration profiles and for Cr surface contents deviating from the nominal one of the bulk. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < x(b) < 9 at.%. In contrast, such threshold behavior of the surface Cr content is absent for Fe-Cr(110) and a nearly homogeneous Cr concentration profile is energetically favorable. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The stability of the Cr surface magnetic moments against bulk Cr content is clarified based on the surface electronic structure.

  • 18.
    Li, Xiaojie
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Taizhou Univ, Dept Phys.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Wei
    Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden..
    Liang, Xiaoqing
    Taizhou Univ, Dept Phys, Taizhou 318000, Zhejiang, Peoples R China..
    Vitos, Levente
    Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden.;Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    First-principles calculations of the cleavage energy in random solid solutions: A case study for TiZrNbHf high-entropy alloy2022In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 212, p. 111575-, article id 111575Article in journal (Refereed)
    Abstract [en]

    The {100} and (110) cleavage energies of body-centered cubic TiZrNbHf high-entropy alloy are calculated using two alloy models: special quasi-random structures (SQSs) and the coherent potential approximation (CPA). The projector augmented wave method, as implemented in the Vienna ab initio simulation package (VASP), in combination with SQSs is adopted to evaluate the impact of local lattice distortions, whereas the exact muffin-tin orbitals (EMTO) method is used in combination with both SQSs and CPA to study the effect of chemical disorder using rigid underlying lattices. The variations of the cleavage energy as a function of surface chemistry and structure from the EMTO and VASP calculations are consistent with each other. Furthermore, the cleavage energies from CPA are in good agreement with those from SQSs, confirming that an averaged supercell approach reproduces well the mean-field CPA results. The alloy's cleavage energies estimated by the rule of mixtures compare well with those from the direct calculations, and the surface chemistry dependence of the cleavage energies is mainly controlled by the number of Nb atoms in the surface terminal layers owing to the large cleavage energy of Nb metal.

  • 19.
    Li, Xiaojie
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Taizhou Univ, Dept Phys, Taizhou 318000, Peoples R China..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Zhao, Jijun
    Dalian Univ Technol, Key Lab Mat Modificat Laser Electron & Ion Beams, Minist Educ, Dalian 116024, Peoples R China..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden.;Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    The influence of temperature on the elastic properties of body-centered cubic reduced activation steels2021In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 197, article id 109282Article in journal (Refereed)
    Abstract [en]

    A first-principles based modeling approach to the effect of temperature on the isothermal single-crystal and polycrystalline elastic parameters of Fe-rich solid solutions is reported. The approach integrates alloy theory for chemical and magnetic disorders with accessible experimental data for the equilibrium volume and ferromagnetic phase transition, and is adopted to predict the temperature-dependent elastic parameters of the body-centered cubic phase of three reduced activation steels, CLAM/CLF-1, F82H, EUROFER97, considered as high-temperature material in power reactors. The predictions are assessed based on available experimental data for a reduced activation steel and both experimental and theoretical data for pure Fe. Alloying effects on the elastic constants relative to pure Fe are found to differ in the magnetically ordered and disordered phases. Contributions due to loss of long-range magnetic order, volume expansion, and entropy are important in determining the temperature dependence of the elastic parameters in all investigated materials. A previously reported, peculiar magneto-volume phenomenon on the equation of state in pure Fe is gradually removed by alloying and magnetic disordering, which requires particular attention when describing the thermo-chemical effects derived from the equation of state in Fe-rich solid solutions.

  • 20.
    Li, Xiaojie
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Taizhou Univ, Dept Phys, Taizhou 318000, Zhejiang, Peoples R China..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Generalized stacking faults energies of face-centered cubic high-entropy alloys: A first-principles study2022In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 145, p. 107556-, article id 107556Article in journal (Refereed)
    Abstract [en]

    Developing high-strength and ductile face-centered cubic (fcc) high-entropy alloys (HEAs) has attracted significant attention. The generalized stacking fault energy (GSFE) is a very useful concept to describe stable and unstable planar defects and their energies on a slip plane. It plays an essential role in designing high performance fcc HEAs and understanding the nanoscale plasticity phenomena. In this work, using first-principles simulations, we investigate the configuration-averaged GSFEs of 29 single-phase fcc HEAs and identify indicators that can be used to tune stacking fault energies. First we determine the equilibrium structural parameters for all considered alloys and compare them with available experimental data. With the obtained GSFEs, we analyze the relationship between the stacking fault energies and materials properties, and investigate scaling relations between planar fault energies and the tendencies to exhibit deformation twinning and transformation to hexagonal close-packed martensite. We find that unstable SFE and shear modulus correlates strongly. Moreover, we reveal that the ratio of intrinsic SFE to unstable SFE, gamma isf/gamma usf, is a characteristic materials measure, and the tendencies to twinning and martensitic transformation rank with it. Our results are expected to be useful for an efficient alloy design and selection of solutes in fcc HEAs.

  • 21.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    First-principles study of the third-order elastic constants and related anharmonic properties in refractory high-entropy alloys2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 142, p. 29-36Article in journal (Refereed)
    Abstract [en]

    The third-order elastic constants (TOECs) and elastic anharmonic behavior in four body-centered cubic refractory high-entropy alloys (HEAs) based on elements of the fourth, fifth, and sixth groups are investigated using density-functional simulations. We find that the values of the TOECs C-111 are the largest in magnitude among the studied six independent TOECs and strongly increase with increasing average valence electron concentration (VEC). Interestingly, the TOEC C-456 undergos a sign change as a function of the VEC. Using the obtained TOECs, we investigate the mode Griineisen constants gamma(i) as well as the low temperature limit (gamma) over bar, derive the long-wavelength acoustic nonlinearity parameters a, and reveal the pressure derivatives of effective elastic constants and polycrystalline moduli as a function of the VEC. Our results show that,6 displays a different directional order along the pure mode [100], [110], and [111] directions for the four considered refractory HEAs. Furthermore, we show that the directional order of,8 is not correlated to the crystal symmetry. With the help of the obtained pressure derivatives of polycrystalline moduli, we predict the low temperature volume expansion coefficient.

  • 22.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Phase stability and micromechanical properties of TiZrHf-based refractory high-entropy alloys: A first-principles study2023In: Physical Review Materials, E-ISSN 2475-9953, Vol. 7, no 11, article id 113604Article in journal (Refereed)
    Abstract [en]

    Endowing room-temperature ductility in refractory high-entropy alloys (RHEAs) is a challenge to their uses in nuclear energy systems, biomedical, and high-temperature applications. Recently, transformation-induced plasticity (TRIP) has been recognized as an effective strategy to simultaneously improve ductility and tensile strength of RHEAs. Hitherto, the design for a TRIP mechanism in RHEAs through material-dependent parameters typically follows empirical approaches. Here, we investigate the alloying effect of several body-centered cubic (bcc) transition metal elements (TM=V, Nb, Cr, Mo, and W) on the phase stability and the micromechanical properties of the TiZrHf alloy using a first-principles method. We show that the addition of the considered TM elements increases the stability of the bcc phase relative to the hexagonal close-packed (hcp) phase and the relative stability between these two phases can be tuned and inverted. We investigate the composition-dependent single-crystal elastic constants for the (TiZrHf)1-xNbx and (TiZrHf)1-xMox alloys and analyze mechanical stability, elastic anisotropy, and polycrystalline moduli. Our results show that the anisotropy of Young's modulus is more pronounced the closer the alloy composition is to the composition where the bcc phase or hcp phase becomes mechanically unstable. We find that the hcp phase has higher shear and Young's moduli than the bcc phase below a critical composition for the Nb or Mo addition, while the bcc phase has larger moduli above the critical composition. Furthermore, our results imply that the d-band filling has a dominant influence on the phase stability and mechanical properties of the alloys.

  • 23.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Third-order elastic constants and anharmonic properties of three fcc high-entropy alloys from first-principles2018In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 764, p. 906-912Article in journal (Refereed)
    Abstract [en]

    Third-order elastic constants (TOECs) are very important for understanding the nonlinear mechanical response of materials and evaluating the anharmonicity of crystal lattices. Here, we are concerned with investigating the six independent TOECs and related anharmonic properties of three face-centered cubic (fcc) high-entropy alloys (HEAs), namely CrFeCoNi, CrMnFeCoNi, and Cr10Mn40Fe40C10, using density-functional simulations. To benchmark computational accuracy, three ab initio codes are used to obtain the complete set of TOECs for fcc Ni. For the HEAs, we observe that the TOECs C-123 and C-456 are positive, and C-123 is particularly large. The Cauchy relations for the TOECs are partially satisfied for the three studied HEAs. With the help of the derived TOECs, the average TOECs for an isotropic polycrystal are estimated. Using the obtained TOECs, we reveal the pressure derivatives of the effective second-order elastic constants and polycrystalline moduli as well as derive the nonlinearity constant delta. The obtained pressure derivative of bulk modulus agrees very well with the available experimental data for CrMnFeCoNi. For the three considered HEAs, delta along high-symmetry directions orders as delta([011]) > delta([111]) > delta ([100]).

  • 24.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Irving, Douglas L.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Engineering Sciences (SCI), Applied Physics.
    First-principles investigation of the micromechanical properties of fcc-hcp polymorphic high-entropy alloys2018In: Scientific Reports, E-ISSN 2045-2322, Vol. 8, article id 11196Article in journal (Refereed)
    Abstract [en]

    High-entropy alloys offer a promising alternative in several high-technology applications concerning functional, safety and health aspects. Many of these new alloys compete with traditional structural materials in terms of mechanical characteristics. Understanding and controlling their properties are of the outmost importance in order to find the best single-or multiphase solutions for specific uses. Here, we employ first-principles alloy theory to address the micro-mechanical properties of five polymorphic high-entropy alloys in their face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Using the calculated elastic parameters, we analyze the mechanical stability, elastic anisotropy, and reveal a strong correlation between the polycrystalline moduli and the average valence electron concentration. We investigate the ideal shear strength of two selected alloys under shear loading and show that the hcp phase possesses more than two times larger intrinsic strength than that of the fcc phase. The derived half-width of the dislocation core predicts a smaller Peierls barrier in the fcc phase confirming its increased ductility compared to the hcp one. The present theoretical findings explain a series of important observations made on dual-phase alloys and provide an atomic-level knowledge for an intelligent design of further high-entropy materials.

  • 25.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. North Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Irving, Douglas L.
    North Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA..
    Varga, Lajos K.
    Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Vitos, Levente
    KTH, School of Engineering Sciences (SCI), Applied Physics. Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys2020In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 189, p. 174-187Article in journal (Refereed)
    Abstract [en]

    Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable - although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant crack-tip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixed-mode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.

  • 26.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles prediction of the stacking fault energy of gold at finite temperature2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 135, p. 88-95Article in journal (Refereed)
    Abstract [en]

    The intrinsic stacking fault energy (ISFE) γ is a material parameter fundamental to the discussion of plastic deformation mechanisms in metals. Here, we scrutinize the temperature dependence of the ISFE of Au through accurate first-principles derived Helmholtz free energies employing both the super cell approach and the axial Ising model (AIM). A significant decrease of the ISFE with temperature, −(36–39) % from 0 to 890 K depending on the treatment of thermal expansion, is revealed, which matches the estimate based on the experimental temperature coefficient dγ/dT closely. We make evident that this decrease predominantly originates from the excess vibrational entropy at the stacking fault layer, although the contribution arising from the static lattice expansion compensates it by approximately 60%. Electronic excitations are found to be of minor importance for the ISFE change with temperature. We show that the Debye model in combination with the AIM captures the correct sign but significantly underestimates the magnitude of the vibrational contribution to γ(T). The hexagonal close-packed (hcp) and double hcp structures are established as metastable phases of Au. Our results demonstrate that quantitative agreement with experiments can be obtained if all relevant temperature-induced excitations are considered in first-principles modeling and that the temperature dependence of the ISFE is substantial enough to be taken into account in crystal plasticity modeling.

  • 27.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    Varga, Lajos K.
    Irving, Douglas L.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Tensile and shear loading of four fcc high-entropy alloys: A first-principles study2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094102Article in journal (Refereed)
    Abstract [en]

    Ab initio density-functional calculations are used to investigate the response of four face-centered-cubic (fcc) high-entropy alloys (HEAs) to tensile and shear loading. The ideal tensile and shear strengths (ITS and ISS) of the HEAs are studied by employing first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. We benchmark the computational accuracy against literature data by studying the ITS under uniaxial [110] tensile loading and the ISS for the [11 (2) over tilde](111) shear deformation of pure fcc Ni and Al. For the HEAs, we uncover the alloying effect on the ITS and ISS. Under shear loading, relaxation reduces the ISS by similar to 50% for all considered HEAs. We demonstrate that the dimensionless tensile and shear strengths are significantly overestimated by adopting two widely used empirical models in comparison with our ab initio calculations. In addition, our predicted relationship between the dimensionless shear strength and shear instability are in line with the modified Frenkel model. Using the computed ISS, we derive the half-width of the dislocation core for the present HEAs. Employing the ratio of ITS to ISS, we discuss the intrinsic ductility of HEAs and compare it with a common empirical criterion. We observe a strong linear correlation between the shear instability and the ratio of ITS to ISS, whereas a weak positive correlation is found in the case of the empirical criterion.

  • 28.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhao, J.
    Johansson, Börje
    Uppsala University, Sweden.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Alloying effect on the ideal tensile strength of ferromagnetic and paramagnetic bcc iron2016In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 676, p. 565-574Article in journal (Refereed)
    Abstract [en]

    Using ab initio alloy theory formulated within the exact muffin-tin orbitals theory in combination with the coherent potential approximation, we investigate the ideal tensile strength (ITS) in the [001] direction of bcc ferro-/ferrimagnetic (FFM) and paramagnetic (PM) Fe1-xMx (M = Al, V, Cr, Mn, Co, or Ni) random alloys. The ITS of ferromagnetic (FM) Fe is calculated to be 12.6 GPa, in agreement with available data, while the PM phase turns out to posses a significantly lower value of 0.7 GPa. Alloyed to the FM matrix, we predict that V, Cr, and Co increase the ITS of Fe, while Al and Ni decrease it. Manganese yields a weak non-monotonic alloying behavior. In comparison to FM Fe, the alloying effect of Al and Co to PM Fe is reversed and the relative magnitude of the ITS can be altered more strongly for any of the solutes. All considered binaries are intrinsically brittle and fail by cleavage of the (001) planes under uniaxial tensile loading in both magnetic phases. We show that the previously established ITS model based on structural energy differences proves successful in the PM Fe-alloys but is of limited use in the case of the FFM Fe-based alloys. The different performance is attributed to the specific interplay between magnetism and volume change in response to uniaxial tension. We establish a strong correlation between the compositional effect on the ITS and the one on the shear elastic constant C' for the PM Fe-alloys and briefly discuss the relation between hardenability and the ITS.

  • 29.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhao, Jijun
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden;.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Anomalous ideal tensile strength of ferromagnetic Fe and Fe-rich alloys2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 2Article in journal (Refereed)
    Abstract [en]

    Within the same failure mode, iron has the lowest ideal tensile strength among the transition metals crystallizing in the body-centered cubic structure. Here, we demonstrate that this anomalously low strength of Fe originates partly from magnetism and is reflected in unexpected alloying effects in dilute Fe(M) (M = Al, V, Cr, Mn, Co, Ni) binaries. We employ the structural energy difference and the magnetic pressure to disentangle the magnetic effect on the ideal tensile strength from the chemical effect. We find that the investigated solutes strongly alter the magnetic response of the Fe host from the weak towards a stronger ferromagnetic behavior, which is explained based on single-particle band energies.

  • 30.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhao, Jijun
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ideal strength of random alloys from first principles2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 21, p. 214203-Article in journal (Refereed)
    Abstract [en]

    The all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation was employed to investigate the ideal tensile strengths of elemental V and Mo solids, and V-and Mo-based random solid solutions. Under uniaxial [001] tensile loading, the ideal tensile strength of V is 11.6 GPa and the lattice fails by shear. Assuming isotropic Poisson contraction, the ideal tensile strengths are 26.7 and 37.6 GPa for V in the [111] and [110] directions, respectively. The ideal strength of Mo is 26.7 GPa in the [001] direction and decreases when a few percent of Tc is introduced in Mo. For the V-based alloys, Cr increases and Ti decreases the ideal tensile strength in all principal directions. Adding the same concentration of Cr and Ti to V leads to ternary alloys with similar ideal strength values as that of pure V. The alloying effects on the ideal strength are explained using the electronic band structure.

  • 31.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tian, Fuyang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Science and Technology Beijing, China.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhao, Jijun
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Ab initio-predicted micro-mechanical performance of refractory high-entropy alloys2015In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 12334Article in journal (Refereed)
    Abstract [en]

    Recently developed high-entropy alloys (HEAs) consisting of multiple principal elements represent a new field of metallurgy and have demonstrated appealing properties for a wide range of applications. Using ab initio alloy theory, we reveal the alloying effect on the elastic properties and the ideal tensile strength (ITS) in the [001] direction of four body-centered cubic (bcc) refractory HEAs based on Zr, V, Ti, Nb, and Hf. We find that these HEAs show high elastic anisotropy and large positive Cauchy pressure, suggesting good extrinsic ductility. Starting from ZrNbHf, it is found that the ITS decreases with equimolar Ti addition. On the other hand, if both Ti and V are added to ZrNbHf, the ITS is enhanced by about 42%. An even more captivating effect is the ITS increase by about 170%, if Ti and V are substituted for Hf. The alloying effect on the ITS is explained by the d-band filling. An intrinsic brittle-to-ductile transition is found in terms of the failure mode under uniaxial tension. These investigations suggest that intrinsically ductile HEAs with high ideal strength can be achieved by controlling the proportion of group four elements to group five elements.

  • 32.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wei, Daixiu
    Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai, Miyagi 980-8577, Japan.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lizarrága, Raquel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Micro-mechanical properties of new alternative binders for cemented carbides: CoCrFeNiWx high-entropy alloys2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 820, article id 153141Article in journal (Refereed)
    Abstract [en]

    High-entropy alloys are a new type of materials with excellent properties that offer a great variety of possibilities due to the large degree of freedom in element composition. In particular, CoCrFeNiW alloys have recently attracted a lot of attention due to their potential use in solving the long-standing problem of substituting cobalt in the cemented carbide industry. The lack of experimental and theoretical studies on these multi-components alloys hinders their optimal development. In this work, we aim at filling in this gap by studying their mechanical properties employing first-principles alloy theory and experimental techniques. By using the calculated elastic parameters, we analyzed the mechanical stability, elastic anisotropy, Debye temperature, and derived polycrystalline moduli. Moreover, we fabricated CoCrFeNi and (CoCrFeNi)0.96W0.04 and analyzed them by means of X-ray diffraction and electron backscatter diffraction. The hardness and the Young's modulus were measured. The Young's moduli and the lattice parameters were compared to first principles calculations and good agreement was obtained. Hardness increases with the increment of W composition.

  • 33.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhao, Jijun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic properties of vanadium-based alloys from first-principles theory2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 1, p. 014105-Article in journal (Refereed)
    Abstract [en]

    The effect of Cr and Ti on the fundamental mechanical properties of V-Cr-Ti alloys has been investigated using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The static lattice constant and elastic parameters have been calculated for the body-centered-cubic V1-x-yCrxTiy (0 <= x,y <= 0.1) random solid solution as a function of composition. Our theoretical predictions are in good agreement with the available experimental data. Alloys along the equicomposition region are found to exhibit the largest shear and Young's modulus as a result of the opposite alloying effects obtained for the two cubic shear elastic constants. The classical solid-solution hardening (SSH) model predicts larger strengthening effect in V1-yTiy than in V1-xCrx. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, it is shown that the present theoretical results can account for the variations of DBTT with composition.

  • 34.
    Lizarrága, Raquel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Industrial Production, Royal Institute of Technology, Stockholm SE-100 44, Swede.
    Li, Xiaojie
    Taizhou Univ, Dept Phys, Taizhou 318000, Peoples R China..
    Wei, Daixiu
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Div Mat Theory, Dept Phys & Mat Sci, POB 516, SE-75120 Uppsala, Sweden. Res Inst Solid State Phys & Opt, Wigner Res Ctr Phys, POB 49, H-1525 Budapest, Hungary..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The effect of Si and Ge on the elastic properties and plastic deformation modes in high- and medium-entropy alloys2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 119, no 14, p. 141904-, article id 141904Article in journal (Refereed)
    Abstract [en]

    We employ quantum mechanics modeling to investigate the effects of Ge and Si solute elements on the elastic properties and plastic deformation modes in two families of high-entropy alloys, CoCrFeMnNi and CoCrFeNi, and medium-entropy alloy, CoCrNi. The static lattice constants and single-crystal elastic parameters are calculated for these three face-centered-cubic random solid solutions as a function of composition. Using the elastic constants, we analyzed mechanical stability, derived polycrystalline modulus, and evaluated solid-solution strengthening for these multi-component alloys. We fabricated (CoCrFeNi)(100-x) Si-x (x = 0, 4, 6) and measured the polycrystalline modulus and hardness. The calculated trends for Young's and shear modulus as well as lattice parameters were verified by our measurements. The dependence of generalized stacking fault energy on Ge and Si was studied in detail for the considered multi-component alloys. The competition between various plastic deformation modes was revealed based on effective energy barriers. Our calculations predict that the activated deformation modes in all the alloys studied here are the stacking fault mode (dominant) and the full-slip mode (secondary), and as the concentrations of Ge and Si increase, twining becomes favored.

  • 35.
    Mo, Jin Yong
    et al.
    School of Chemistry and Chemical Engineering, China University of Mining and Technology, Xuzhou, 221116, China; Defense Innovation Institute, Academy of Military Science, Beijing, 100071, China.
    Wan, Yi Xing
    School of Chemistry and Chemical Engineering, China University of Mining and Technology, Xuzhou, 221116, China.
    Zhang, Zhi Bin
    Defense Innovation Institute, Academy of Military Science, Beijing, 100071, China.
    Wang, Xin
    Defense Innovation Institute, Academy of Military Science, Beijing, 100071, China.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Shen, Bao Long
    School of Materials Science and Engineering, Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, Nanjing, 211189, China.
    Liang, Xiu Bing
    Defense Innovation Institute, Academy of Military Science, Beijing, 100071, China.
    First-principle prediction of structural and mechanical properties in NbMoTaWRex refractory high-entropy alloys with experimental validation2022In: Rare Metals, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 41, no 10, p. 3343-3350Article in journal (Refereed)
    Abstract [en]

    In this work, the effect of Re alloying on the phase composition, crystal structure, and mechanical properties of NbMoTaWRex (x = 0, 0.27, 0.57, 0.92, 1.33) refractory high-entropy alloys (RHEAs) were systematically investigated by combining the calculation of phase diagram (CALPHAD), first-principle calculations and experiment. The theoretical predictions showed good consistency with the experimental results. As the increase in Re content, the theoretical results showed that all considered alloys have a single body-centered cubic (bcc) structure and the lattice constant and ductility were decreased, while the elastic moduli and hardness were improved. To avoid extreme brittleness, a strategic suggestion was given for the design of Re-containing RHEAs in the future.

  • 36.
    Mo, Jinyong
    et al.
    China Univ Min & Technol, Sch Chem & Chem Engn, Xuzhou 221116, Peoples R China..
    Liang, Xiubing
    Acad Mil Sci, Def Innovat Inst, Beijing 100071, Peoples R China..
    Shen, Baolong
    Southeast Univ, Sch Mat Sci & Engn, Jiangsu Key Lab Adv Metall Mat, Nanjing 211189, Peoples R China..
    Wan, Yixing
    China Univ Min & Technol, Sch Chem & Chem Engn, Xuzhou 221116, Peoples R China..
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermocalc Software AB, Rasundavagen 18A, S-16967 Solna, Sweden..
    Zhang, Zhibin
    Acad Mil Sci, Def Innovat Inst, Beijing 100071, Peoples R China..
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Local lattice distortions, phase stability, and mechanical properties of NbMoTaWHfx alloys: A combined theoretical and experimental study2023In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 217, article id 111891Article in journal (Refereed)
    Abstract [en]

    Refractory high-entropy alloys (RHEAs) are of growing interest due to their potentially superior mechanical performances at elevated temperatures. Inherent lattice distortions are believed to be a major contributor to strength in solid solution phases of RHEAs. Here, we investigate the NbMoTaWHfx alloy series (x = 0, 0.27, 0.57, 0.92, 1.33, 1.82) using first-principles simulations, thermodynamic modeling, and experimental techniques. The first-principles results suggest that Hf alloying is an effective means to enhance atomic-scale lattice distortions in BCC NbMoTaWHfx solid solutions. X-ray diffraction on prepared as-cast samples shows that the alloys with Hf content x <= 0.92 are single phase BCC alloys, whereas a dual BCC phase microstructure is observed for x = 1.33 and 1.82. Elemental mappings from scanning electron microscopy for the dual-phase alloys are checked with predictions from thermodynamic modeling for equilibrium and non-equilibrium solidifications. Room-temperature compressive mechanical tests reveal that yield and ultimate strengths increase strongly with the addition of Hf and saturate for x > 0.92, whereas the compressive plasticity is slightly improved by Hf but remains limited. We predict the compositional effects on poly-crystal elastic moduli for the constituent BCC phases and the dual-phase composites and find a linear behavior between modulus-normalized yield strength and lattice distortion on average.

  • 37.
    Qin, Gang
    et al.
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    Chen, Ruirun
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China.;Harbin Inst Technol, State Key Lab Adv Welding & Joining, Harbin 150001, Heilongjiang, Peoples R China..
    Liaw, Peter K.
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Ga, Yanfei
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zheng, Huiting
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    Wang, Liang
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    Su, Yanqing
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    Guo, Jingjie
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    Fu, Hengzhi
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Heilongjiang, Peoples R China..
    A novel face-centered-cubic high-entropy alloy strengthened by nanoscale precipitates2019In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 172, p. 51-55Article in journal (Refereed)
    Abstract [en]

    A new single-phase face-centered-cubic (FCC) Co9Cr7Cu36Mn25Ni23 [atomic percent, similar hereinafter] high-entropy alloy (HEA) was prepared by arc melting. A uniform distribution of nanometer-sized precipitates was achieved. The tensile yield strength, ultimate tensile strength, and elongation were 401 MPa, 700 MPa, and 36%, respectively. The energy-dispersive spectrometer results showed that the nano-precipitates were rich in Co and Cr elements. Moreover, the crystal-forming behavior and the nanoscale-precipitates-forming mechanism were revealed. Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 38.
    Qin, Gang
    et al.
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Chen, Ruirun
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Liaw, Peter K.
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Gao, Yanfei
    Univ Tennessee, Dept Mat Sci & Engn, Knoxville, TN 37996 USA..
    Wang, Liang
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Su, Yanqing
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Ding, Hongsheng
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Guo, Jingjie
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    An as-cast high-entropy alloy with remarkable mechanical properties strengthened by nanometer precipitates2020In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 12, no 6, p. 3965-3976Article in journal (Refereed)
    Abstract [en]

    High-entropy alloys (HEAs) with good ductility and high strength are usually prepared by a combination of forging and heat-treatment processes. In comparison, the as-cast HEAs typically do not reach strengths similar to those of HEAs produced by the forging and heat-treatment processes. Here we report a novel equiatomic-ratio CoCrCuMnNi HEA prepared by vacuum arc melting. We observe that this HEA has excellent mechanical properties, i.e., a yield strength of 458 MPa, and an ultimate tensile strength of 742 MPa with an elongation of 40%. Many nanometer precipitates (5-50 nm in size) and domains (5-10 nm in size) are found in the inter-dendrite and dendrite zones of the produced HEA, which is the key factor for its excellent mechanical properties. The enthalpy of mixing between Cu and Mn, Cr, Co, or Ni is higher than those of mixing between any two of Cr, Co, Ni and Mn, which leads to the separation of Cu from the CoCrCuMnNi HEA. Furthermore, we reveal the nanoscale-precipitate-phase-forming mechanism in the proposed HEA.

  • 39.
    Qin, Gang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Chen, Ruirun
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China.;Harbin Inst Technol, State Key Lab Adv Welding & Joining, Harbin 150001, Peoples R China..
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermocalc Software.
    Yan, Yan
    Harbin Inst Technol, Natl Key Lab Precis Hot Proc Met, Harbin 150001, Peoples R China..
    Li, Xiaojie
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Experimental and theoretical investigations on the phase stability and mechanical properties of Cr7Mn25Co9Ni23Cu36 high-entropy alloy2021In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 208, article id 116763Article in journal (Refereed)
    Abstract [en]

    Understanding the mechanisms of phase formation and their influence on the mechanical behavior is crucial for materials used in structural applications. Here, the phase decomposition under heat treatment in the Cr7Mn25Co9Ni23Cu36 (atomic percentage) high-entropy alloy and how secondary phases formed affect its tensile mechanical response are reported. The microstructural analysis shows that heat treatment at 800 degrees C /2 h and 600 degrees C /8 h led to the formation of sigma phase, but the sigma phase was not observed for 2 h heat treatment at 600 degrees C and below. The experimentally observed thermal stability and phases are compared to the calculated phase diagram and rationalized by recourse to thermodynamics and kinetics. The mechanism of phase decomposition is discussed based on ab initio calculations, indicating that decomposition into two solid solution phases is energetically preferred over a single solid solution phase with nominal composition.

  • 40.
    Schönecker, Stephan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Wei
    Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Effect of strain on generalized stacking fault energies and plastic deformation modes in fcc-hcp polymorphic high-entropy alloys: A first-principles investigation2021In: Physical Review Materials, E-ISSN 2475-9953, Vol. 5, no 7, article id 075004Article in journal (Refereed)
    Abstract [en]

    The generalized stacking fault energy (GSFE) is a material property that can provide invaluable insights into describing nanoscale plasticity phenomena in crystalline materials. Lattice strains have been suggested to influence such phenomena. Here, the GSFE curves for sequential faulting pathways in dual phase [face-centered cubic (fcc) and hexagonal close-packed (hcp)] Cr20Mn20Fe20Co20Ni20, Cr25Fe25Co25Ni25, Cr20Mn20Fe34Co20Ni6, Cr20Mn20Fe30Co20Ni10, and Cr10Mn30Fe50Co10 high-entropy alloys are investigated on {111}(fcc) and (0002)(hcp) close-packed planes using density-functional calculations. The dependence of GSFEs on imposed volumetric and longitudinal lattice strains is studied in detail for Cr20Mn20Fe20Co20Ni20 and Cr10Mn30Fe50Co10. The competition between various plastic deformation modes is discussed for both phases based on effective energy barriers determined from the calculated GSFEs and compared with experimentally observed deformation mechanisms. The intrinsic stacking fault energy, unstable stacking fault energy, and unstable twinning fault energy are found to be closely related in how they are affected by applied strain. The ratio of two of these planar fault energies can thus serve as characteristic material property. An inverse relationship between the intrinsic stacking fault energy in the hcp phase and the axial ratio (c/a)(hcp) is revealed and explained via band theory.

  • 41.
    Schönecker, Stephan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Li, Xiaojie
    Taizhou Univ, Dept Phys, Taizhou 318000, Zhejiang, Peoples R China..
    Wei, Daixiu
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Nozaki, Shogo
    Tohoku Univ, Dept Mat Sci, 6-6-02 Aramaki Aza Aoba, Sendai, Miyagi 9808579, Japan..
    Kato, Hidemi
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties. Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Harnessing elastic anisotropy to achieve low-modulus refractory high-entropy alloys for biomedical applications2022In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 215, article id 110430Article in journal (Refereed)
    Abstract [en]

    A high-priority target in the design of new metallic materials for load-bearing implant applications is the reduction of Young's modulus approximating that of cortical bone in the predominant loading direction. Here, we explore how directionally preferential bulk elastic properties of implant materials are achieved by harnessing elastic anisotropy. Specifically focusing on recently proposed biocompatible refractory high-entropy alloys (RHEAs) in the body-centered cubic structure, we conduct systematic densityfunctional theory calculations to investigate the single-crystal elastic properties of 21 Ti-containing RHEAs. Our results provide evidence that the valence electron count has a dominant influence on elastic anisotropy and crystal directions of low Young's modulus and high torsion modulus in the RHEAs. By means of modeling the orientation distribution function for crystallographic texture, we examine the effect of non-random texture on the anisotropic poly-crystalline Young's modulus and torsion modulus with varying texture sharpness. We adopt fiber textures that can result from rolling and distinct texture orientations that can form during rapid directional solidification. We discuss the potential for lowering Young's modulus in the RHEAs by using single crystals or textured aggregates. Furthermore, we prepare four of the theoretically considered alloys by arc-melting and report their lattice parameters, quasi isotropic Young's moduli, and Wickers hardnesses.

  • 42.
    Schönecker, Stephan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kwon, Se Kyun
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Thermal surface free energy and stress of iron2015In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 14860Article in journal (Refereed)
    Abstract [en]

    Absolute values of surface energy and surface stress of solids are hardly accessible by experiment. Here, we investigate the temperature dependence of both parameters for the (001) and (110) surface facets of body-centered cubic Fe from first-principles modeling taking into account vibrational, electronic, and magnetic degrees of freedom. The monotonic decrease of the surface energies of both facets with increasing temperature is mostly due to lattice vibrations and magnetic disorder. The surface stresses exhibit nonmonotonic behaviors resulting in a strongly temperature dependent excess surface stress and surface stress anisotropy.

  • 43.
    Schönecker, Stephan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Atomic long-range order effects on Curie temperature and adiabatic spin-wave dynamics in strained Fe-Co alloy films2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 6, article id 064410Article in journal (Refereed)
    Abstract [en]

    The strained Fe-Co alloy in body-centered tetragonal (bct) structure has raised considerable interest due to its giant uniaxial magnetocrystalline anisotropy energy. On the basis of the classical Heisenberg Hamiltonian with ab initio interatomic exchange interactions, we perform a theoretical study of fundamental finite temperature magnetic properties of Fe1-xCox alloy films as a function of three variables: chemical composition 0.3 <= x <= 0.8, bct geometry [a, c(a)] arising from in-plane strain and associated out-of-plane relaxation, and atomic long-range order (ALRO). The Curie temperatures T-C(x, a) obtained from Monte Carlo simulations display a competition between a pronounced dependence on tetragonality, strong ferromagnetism in the Co-rich alloy, and the beginning instability of ferromagnetic order in the Fe-rich alloy when c/a -> root 2. Atomic ordering enhances T-C and arises mainly due to different distributions of atoms in neighboring coordination shells rather than altering exchange interactions significantly. We investigate the ordering effect on the shape of the adiabatic spin-wave spectrum for selected pairs (x, a). Our results indicate that long-wavelength acoustic spin-wave excitations show dependencies on x, a, and ALRO similar to those of T-C. The directional anisotropy of the spin-wave stiffness d(x, a) peaks in narrow ranges of composition and tetragonality. ALRO exhibits a strong effect on d for near equiconcentration Fe-Co. We also discuss our findings in the context of employing Fe-Co as perpendicular magnetic recording medium.

  • 44.
    Schönecker, Stephan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Richter, Manuel
    IFW Dresden, D-01069 Dresden, Germany.;Dresden Ctr Computat Mat Sci, D-01069 Dresden, Germany..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lattice dynamics and metastability of fcc metals in the hcp structure and the crucial role of spin-orbit coupling in platinum2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 22, article id 224305Article in journal (Refereed)
    Abstract [en]

    We investigate the lattice dynamical properties of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au in the nonequilibrium hcp structure by means of density-functional simulations, wherein spin-orbit coupling (SOC) was considered for Ir, Pt, and Au. The determined dynamical properties reveal that all eight elements possess a metastable hcp phase at zero temperature and pressure. The hcp Ni, Cu, Rh, Pd, and Au previously observed in nanostructures support this finding. We make evident that the inclusion of SOC is mandatory for an accurate description of the phonon dispersion relations and dynamical stability of hcp Pt. The underlying sensitivity of the interatomic force constants is ascribed to a SOC-induced splitting of degenerate band states accompanied by a pronounced reduction of electronic density of states at the Fermi level. To give further insight into the importance of SOC in Pt, we (i) focus on phase stability and examine a lattice transformation related to optical phonons in the hcp phase and (ii) focus on the generalized stacking fault energy (GSFE) of the fcc phase pertinent to crystal plasticity. We show that the intrinsic stable and unstable fault energies of the GSFE scale as in other common fcc metals, provided that the spin-orbit interaction is taken into account.

  • 45.
    Temesi, Otto
    et al.
    H ION Res Dev & Innovat Ltd, Konkoly Thege Mikl Ut 29-33, H-1121 Budapest, Hungary.;Eotvos Lorand Univ, Dept Mat Phys, Pazmany Peter Setany 1-A, H-1117 Budapest, Hungary..
    Varga, Lajos K.
    Inst Solid State Phys & Opt, Wigner Res Ctr Phys, Konkoly Thege Mikl Ut 29-33, H-1121 Budapest, Hungary..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Inst Solid State Phys & Opt, Wigner Res Ctr Phys, Konkoly Thege Mikl Ut 29-33, H-1121 Budapest, Hungary..
    Chinh, Nguyen Q.
    Eotvos Lorand Univ, Dept Mat Phys, Pazmany Peter Setany 1-A, H-1117 Budapest, Hungary..
    Estimation of Shear Modulus and Hardness of High-Entropy Alloys Made from Early Transition Metals Based on Bonding Parameters2023In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 16, no 6, p. 2311-, article id 2311Article in journal (Refereed)
    Abstract [en]

    The relationship between the tendencies towards rigidity (measured by shear modulus, G) and hardness (measured by Vickers hardness, HV) of early transition metal (ETM)-based refractory high-entropy alloys (RHEA) and bond parameters (i.e., valence electron concentration (VEC), enthalpy of mixing (?H-mix)) was investigated. These bond parameters, VEC and ?H-mix, are available from composition and tabulated data, respectively. Based on our own data (9 samples) and those available from the literatures (47 + 27 samples), it seems that for ETM-based RHEAs the G and HV characteristics have a close correlation with the bonding parameters. The room temperature value of G and HV increases with the VEC and with the negative value of ?H-mix. Corresponding equations were deduced for the first time through multiple linear regression analysis, in order to help design the mechanical properties of ETM refractory high-entropy alloys.

  • 46. Wei, D.
    et al.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jiang, J.
    Heng, W.
    Koizumi, Y.
    Choi, W. -M
    Lee, B. -J
    Kim, H. S.
    Kato, H.
    Chiba, A.
    Novel Co-rich high performance twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) high-entropy alloys2019In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 165, p. 39-43Article in journal (Refereed)
    Abstract [en]

    The equiatomic CoCrMnNiFe high-entropy alloy (HEA) has attracted much attention owing to its exceptional mechanical properties. Here, we designed novel face-centered cubic (fcc) phase Co-rich non-equiatomic CoCrMnNiFe HEAs with tensile properties superior to the counterparts, derived from lowering stacking fault energy (SFE) via modifying constituent concentrations. The decrease of Mn, Ni, Fe meanwhile increase of Co, Cr concentrations does reduce the SFE value, based on ab initio and thermodynamics calculations. Hereinto, Co 35 Cr 20 Mn 15 Ni 15 Fe 15 and Co 35 Cr 25 Mn 15 Ni 15 Fe 10 HEAs overcame the strength-ductility trade-off, contributing to twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) effects, respectively. The present study sheds light on developing high performance HEAs.

  • 47.
    Wei, Daixiu
    et al.
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Gong, Wu
    Japan Atom Energy Agcy, J PARC Ctr, 2-4 Shirakata, Tokai, Ibaraki 3191195, Japan..
    Tsuru, Tomohito
    Japan Atom Energy Agcy, Nucl Sci & Engn Ctr, 2-4 Shirakata, Ibaraki 3191195, Japan.;Kyoto Univ, Sakyo Ku, Elements Strategy Initiat Struct Mat, Yoshida Honmachi, Kyoto 6068501, Japan.;Japan Sci & Technol Agcy, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 3320012, Japan..
    Lobzenko, Ivan
    Japan Atom Energy Agcy, Nucl Sci & Engn Ctr, 2-4 Shirakata, Ibaraki 3191195, Japan..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Harjo, Stefanus
    Japan Atom Energy Agcy, J PARC Ctr, 2-4 Shirakata, Tokai, Ibaraki 3191195, Japan..
    Kawasaki, Takuro
    Japan Atom Energy Agcy, J PARC Ctr, 2-4 Shirakata, Tokai, Ibaraki 3191195, Japan..
    Do, Hyeon-Seok
    Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Bae, Jae Wung
    Pukyong Natl Univ, Dept Met Engn, Busan 48513, South Korea..
    Wagner, Christian
    Ruhr Univ Bochum, Inst Werkstoffe, Univ Str 150, D-44801 Bochum, Germany..
    Laplanche, Guillaume
    Ruhr Univ Bochum, Inst Werkstoffe, Univ Str 150, D-44801 Bochum, Germany..
    Koizumi, Yuichiro
    Osaka Univ, Grad Sch Engn, Div Mat & Mfg Sci, 2-1 Yamadaoka, Suita, Osaka 5650871, Japan..
    Adachi, Hiroki
    Univ Hyogo, Grad Sch Engn, Dept Mat & Synchrotron Radiat Engn, Himeji, Hyogo 6712280, Japan..
    Aoyagi, Kenta
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Chiba, Akihiko
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Lee, Byeong-Joo
    Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Kim, Hyoung Seop
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan.;Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Kato, Hidemi
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys2022In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 159, article id 103443Article in journal (Refereed)
    Abstract [en]

    Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.

  • 48.
    Wei, Daixiu
    et al.
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan.;MIT, Dept Mat Sci & Engn, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Heng, Weicheng
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan.;Tohoku Univ, Dept Mat Proc, Sendai, Miyagi, Japan..
    Koizumi, Yuichiro
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    He, Feng
    MIT, Dept Mat Sci & Engn, 77 Massachusetts Ave, Cambridge, MA 02139 USA.;Northwestern Polytech Univ, State Key Lab Solidificat Proc, Xian, Shaanxi, Peoples R China..
    Choi, Won-Mi
    Pohan Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohan, South Korea..
    Lee, Byeong-Joo
    Pohan Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohan, South Korea..
    Kim, Hyoung Seop
    Pohan Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohan, South Korea..
    Kato, Hidemi
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Chiba, Akihiko
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Novel Co-rich high entropy alloys with superior tensile properties2019In: Materials Research Letters, E-ISSN 2166-3831, Vol. 7, no 2, p. 82-88Article in journal (Refereed)
    Abstract [en]

    We developed a series of Co-rich CoxCr25(FeNi)(75-x) (x = 35, 45, 55, 65) high entropy alloys with improved strength and/or ductility, derived from lowering the stacking fault energy (SFE) and reducing the fcc phase stability of the equiatomic CoCrFeNi alloy. Thermodynamics and ab initio calculations demonstrated that increasing Co while decreasing Fe and Ni concentrations lower the SFE and reduce the fcc phase stability. The Co35Cr25Fe20Ni20 and Co45Cr25Fe15Ni15 alloys with single fcc phase, exhibit superior tensile properties, contributing to the twinning and fcc -> hcp martensitic transformation. The present study offers a guideline for designing high-performance high entropy alloys. [GRAPHICS] IMPACT STATEMENT A series of novel Co-rich non-equiatomic high entropy alloys with enhanced tensile properties were developed by lowering the stacking fault energy and reducing the phase stability of equiatomic CoCrFeNi alloy.

  • 49.
    Wei, Daixiu
    et al.
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jiang, Jing
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Choi, Won-Mi
    Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Lee, Byeong-Joo
    Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Kim, Hyoung Seop
    Pohang Univ Sci & Technol POSTEC, Dept Mat Sci & Engn, Pohang 37673, South Korea..
    Chiba, Akihiko
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Kato, Hidemi
    Tohoku Univ, Inst Mat Res, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan..
    Development of strong and ductile metastable face-centered cubic single-phase high-entropy alloys2019In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 181, p. 318-330Article in journal (Refereed)
    Abstract [en]

    Face-centered cubic (fcc)-phase high-entropy alloys (HEAs) have attracted much academic interest, with the stacking fault energy (SFE) playing an important role in regulating their mechanical behaviors. Here, we revealed the principles for regulating both the elastic and plastic behaviors by composition modification and Mo addition in an fcc-phase quaternary CoCrFeNi system with the assistance of ab initio and thermodynamics calculations. An increase in Co content and a decrease in Fe and Ni contents reduced the fcc phase stability and SFE, but enhanced the elastic modulus, anisotropy, and lattice friction stress. A minor substitution of Co by Mo increased the lattice constant, but decreased the SFE and elastic modulus. Based on these findings, we developed a series of strong and ductile metastable fcc-phase CoxCr25(FeNi)(70-x)Mo-5 (x = 30, 40, 50) HEAs with mechanical properties superior to those of the CoCrFeNi HEM. The careful investigation revealed that the enhanced mechanical properties are due to the Mo-addition-induced strengthening accompanied with a low-SFE-induced restriction of planar behavior of dislocations, mechanical twinning, and strain-induced martensitic transformation. The findings shed light on the development of high-performance HEAs.

  • 50.
    Xu, W. W.
    et al.
    Xiamen Univ, Sch Aerosp Engn, Xiamen 361005, Peoples R China..
    Xiong, Z. Y.
    Xiamen Univ, Sch Aerosp Engn, Xiamen 361005, Peoples R China..
    Li, Z. N.
    Xiamen Univ, Sch Aerosp Engn, Xiamen 361005, Peoples R China..
    Gao, X.
    Xiamen Univ, Sch Aerosp Engn, Xiamen 361005, Peoples R China..
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Yang, T.
    City Univ Hong Kong, Dept Mat Sci & Engn, Hong Kong, Peoples R China.;City Univ Hong Kong, Hong Kong Inst Adv study, Hong Kong, Peoples R China..
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.
    Liu, C. T.
    City Univ Hong Kong, Dept Mat Sci & Engn, Hong Kong, Peoples R China.;City Univ Hong Kong, Hong Kong Inst Adv study, Hong Kong, Peoples R China..
    Atomic origins of the plastic deformation micro-mechanisms of ?/??: FeCoNiAlTi high-entropy alloys2022In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 158, p. 103439-, article id 103439Article in journal (Refereed)
    Abstract [en]

    The gamma/gamma' FeCoNiAlTi high-entropy alloys (HEAs) break the strength-ductility trade-off and possess an excellent combination of strength and ductility. However, lack of atomic-level understanding of plastic deformation behaviors restricts the exploration of full capacities of the FeCoNiAlTi HEAs. By computing the generalized stacking fault energies (GSFEs) of the gamma and gamma' phases, the relationships between planar stacking faults and work-hardening capacities, and the effect of chemical concentration and grain orientation on the deformation mechanisms were explored in depth for the FeCoNiAlTi HEAs. Our results demonstrate that the multicomponent nature lowers the GSFEs of the matrix but enhances those of the precipitate to achieve the strength-ductility balance of the HEA. An active factor (epsilon) defined as gamma isf/gamma apb (gamma isf: intrinsic stacking fault energy, gamma apb: anti-phase boundary energy) was introduced to bridge activation of microbands (MBs) and planar stacking faults in the gamma/gamma' alloys. Tuning a suitable low epsilon around 0.2 is an efficient strategy for acquiring the extended MBs-induced plasticity. Analyzing the individual/synergetic contribution of the principal elements to the GSFEs-related properties, we find that increasing the amount of Co and Ti promotes the strength-ductility balance and facilitates the MB activation by altering the GSFEs of both gamma and gamma'. Based on our comprehensive analysis, it is concluded that raising the Co/Fe ratio or lowing the Al/Ti ratio benefits the achievement of the desired mechanical properties of the FeCoNiAlTi HEA.

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