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Li, Xiaoqing
Publications (10 of 57) Show all publications
Cheng, Q., Mo, J., Li, X. & Xu, X. (2023). A revisit to the role of Mo in an MP35N superalloy: An experimental and theoretical study. Journal of Materials Science & Technology, 157, 60-70
Open this publication in new window or tab >>A revisit to the role of Mo in an MP35N superalloy: An experimental and theoretical study
2023 (English)In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 157, p. 60-70Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Mo addition, Solid solution strengthening, Grain boundary softening, Local lattice distortion, First-principles simulations, Stacking fault energy, Deformation twin
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-327442 (URN)10.1016/j.jmst.2023.01.017 (DOI)000982532200001 ()2-s2.0-85151489098 (Scopus ID)
Note

QC 20230529

Available from: 2023-05-29 Created: 2023-05-29 Last updated: 2023-05-29Bibliographically approved
Hu, J., Wang, W., Xie, L., Sun, G., Shen, H., Li, X., . . . Xiao, H. (2023). Effects of NH4+ doping on the hydrogen storage properties of metal hydrides. International journal of hydrogen energy, 48(50), 19153-19159
Open this publication in new window or tab >>Effects of NH4+ doping on the hydrogen storage properties of metal hydrides
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2023 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 48, no 50, p. 19153-19159Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
First-principles calculation, Hydrogen storage, Metal hydrides, NH 4 +, Thermal stability
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-330958 (URN)10.1016/j.ijhydene.2023.01.348 (DOI)001013100300001 ()2-s2.0-85148723976 (Scopus ID)
Note

QC 20230707

Available from: 2023-07-07 Created: 2023-07-07 Last updated: 2023-09-05Bibliographically approved
Temesi, O., Varga, L. K., Li, X., Vitos, L. & Chinh, N. Q. (2023). Estimation of Shear Modulus and Hardness of High-Entropy Alloys Made from Early Transition Metals Based on Bonding Parameters. Materials, 16(6), 2311, Article ID 2311.
Open this publication in new window or tab >>Estimation of Shear Modulus and Hardness of High-Entropy Alloys Made from Early Transition Metals Based on Bonding Parameters
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2023 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 16, no 6, p. 2311-, article id 2311Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI AG, 2023
Keywords
Early Transition Metals (ETM), Refractory High Entropy Alloy (RHEA), shear modulus (G), valence electron concentration (VEC), enthalpy of mixing (?H-mix), Vickers hardness (HV)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-326151 (URN)10.3390/ma16062311 (DOI)000959729700001 ()36984190 (PubMedID)2-s2.0-85152045609 (Scopus ID)
Note

QC 20230425

Available from: 2023-04-25 Created: 2023-04-25 Last updated: 2023-04-25Bibliographically approved
Mo, J., Liang, X., Shen, B., Wan, Y., Mao, H., Zhang, Z., . . . Li, X. (2023). Local lattice distortions, phase stability, and mechanical properties of NbMoTaWHfx alloys: A combined theoretical and experimental study. Computational materials science, 217, Article ID 111891.
Open this publication in new window or tab >>Local lattice distortions, phase stability, and mechanical properties of NbMoTaWHfx alloys: A combined theoretical and experimental study
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2023 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 217, article id 111891Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2023
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-323764 (URN)10.1016/j.commatsci.2022.111891 (DOI)000912375600001 ()2-s2.0-85141473634 (Scopus ID)
Note

QC 20230215

Available from: 2023-02-15 Created: 2023-02-15 Last updated: 2023-02-15Bibliographically approved
Li, X. (2023). Phase stability and micromechanical properties of TiZrHf-based refractory high-entropy alloys: A first-principles study. Physical Review Materials, 7(11), Article ID 113604.
Open this publication in new window or tab >>Phase stability and micromechanical properties of TiZrHf-based refractory high-entropy alloys: A first-principles study
2023 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 7, no 11, article id 113604Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-340977 (URN)10.1103/PhysRevMaterials.7.113604 (DOI)001110060900006 ()2-s2.0-85178063293 (Scopus ID)
Note

QC 20231218

Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2024-01-16Bibliographically approved
Xu, W. W., Xiong, Z. Y., Li, Z. N., Gao, X., Li, W., Yang, T., . . . Liu, C. T. (2022). Atomic origins of the plastic deformation micro-mechanisms of ?/??: FeCoNiAlTi high-entropy alloys. International journal of plasticity, 158, 103439, Article ID 103439.
Open this publication in new window or tab >>Atomic origins of the plastic deformation micro-mechanisms of ?/??: FeCoNiAlTi high-entropy alloys
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2022 (English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 158, p. 103439-, article id 103439Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
High -entropy alloys, L1 2?? precipitate, Stacking faults energy, Deformation mechanism, Density -functional theory
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-321308 (URN)10.1016/j.ijplas.2022.103439 (DOI)000874924700001 ()2-s2.0-85140291159 (Scopus ID)
Note

QC 20221111

Available from: 2022-11-11 Created: 2022-11-11 Last updated: 2022-11-11Bibliographically approved
Mo, J. Y., Wan, Y. X., Zhang, Z. B., Wang, X., Li, X., Shen, B. L. & Liang, X. B. (2022). First-principle prediction of structural and mechanical properties in NbMoTaWRex refractory high-entropy alloys with experimental validation. Rare Metals, 41(10), 3343-3350
Open this publication in new window or tab >>First-principle prediction of structural and mechanical properties in NbMoTaWRex refractory high-entropy alloys with experimental validation
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2022 (English)In: Rare Metals, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 41, no 10, p. 3343-3350Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer Nature, 2022
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-329062 (URN)10.1007/s12598-022-02054-6 (DOI)000842592600001 ()2-s2.0-85136214290 (Scopus ID)
Note

QC 20230614

Available from: 2023-06-14 Created: 2023-06-14 Last updated: 2023-06-14Bibliographically approved
Li, X., Schönecker, S., Li, X., Li, W., Liang, X. & Vitos, L. (2022). First-principles calculations of the cleavage energy in random solid solutions: A case study for TiZrNbHf high-entropy alloy. Computational materials science, 212, 111575, Article ID 111575.
Open this publication in new window or tab >>First-principles calculations of the cleavage energy in random solid solutions: A case study for TiZrNbHf high-entropy alloy
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2022 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 212, p. 111575-, article id 111575Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
High-entropy alloy, Cleavage energy, First-principles calculations
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-315899 (URN)10.1016/j.commatsci.2022.111575 (DOI)000822908900006 ()2-s2.0-85132213115 (Scopus ID)
Note

QC 20220728

Available from: 2022-07-28 Created: 2022-07-28 Last updated: 2022-07-28Bibliographically approved
Li, X., Schönecker, S., Vitos, L. & Li, X. (2022). Generalized stacking faults energies of face-centered cubic high-entropy alloys: A first-principles study. Intermetallics (Barking), 145, 107556, Article ID 107556.
Open this publication in new window or tab >>Generalized stacking faults energies of face-centered cubic high-entropy alloys: A first-principles study
2022 (English)In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 145, p. 107556-, article id 107556Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Generalized stacking faults energies, Face -centered cubic, High-entropy alloys, Twinnability, Martensitic transformation
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-313505 (URN)10.1016/j.intermet.2022.107556 (DOI)000794294400002 ()2-s2.0-85127111106 (Scopus ID)
Note

QC 20220607

Available from: 2022-06-07 Created: 2022-06-07 Last updated: 2022-06-25Bibliographically approved
Schönecker, S., Li, X., Wei, D., Nozaki, S., Kato, H., Vitos, L. & Li, X. (2022). Harnessing elastic anisotropy to achieve low-modulus refractory high-entropy alloys for biomedical applications. Materials & design, 215, Article ID 110430.
Open this publication in new window or tab >>Harnessing elastic anisotropy to achieve low-modulus refractory high-entropy alloys for biomedical applications
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 215, article id 110430Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Refractory high-entropy alloy, Young's modulus, Elastic anisotropy, Crystallographic texture, Density-functional theory
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-310062 (URN)10.1016/j.matdes.2022.110430 (DOI)000761234900001 ()2-s2.0-85124409411 (Scopus ID)
Note

QC 20220322

Available from: 2022-03-22 Created: 2022-03-22 Last updated: 2022-06-25Bibliographically approved
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