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  • 1.
    Al-Zoubi, Noura
    et al.
    Tafila Tech Univ, Dept Appl Phys, Tafila, Jordan..
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic properties of 4d transition metal alloys: Values and trends2019Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 159, s. 273-280Artikel i tidskrift (Refereegranskat)
    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.

  • 2.
    Dai, J. H.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Harbin Inst Technol Weihai, Sch Mat Sci & Engn, 2 West Wenhua Rd, Weihai 264209, Peoples R China..
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Song, Y.
    Harbin Inst Technol Weihai, Sch Mat Sci & Engn, 2 West Wenhua Rd, Weihai 264209, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Theoretical investigation of the phase stability and elastic properties of TiZrHfNb-based high entropy alloys2019Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 182, artikel-id UNSP 108033Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First principles calculations are performed to study the effects of alloying elements (X = Al, Si, Sc, V, Cr, Mn, Cu, Zn, Y. Mo, Ta, W and Re) on the phase stability and elastic properties of TiZrHfNb refractory high entropy alloys. Both equimolar and non-equimolar alloys are considered. It is shown that the calculated lattice parameters, phase stability and elastic moduli of equimolar TiZrHfNbX are consistent with the available experimental and theoretical results. The substitutions of alloying elements at Ti, Zr, and Hf sites with various contents show similar effects on the phase stability and elastic properties of the TiZrHINb-based alloys. The substitutions on Nb site are found to generally decrease the stability of body centered cubic phase. Close connections between the charge densities at the Wigner-Seitz cell boundary and the bulk moduli of TiZrHfNb-based alloys are found. The present results provide a quantitative model for exploring the phase stability and elastic properties of TiZrHINb-based alloys from the electronic structure viewpoint. Elsevier Ltd.

  • 3. Dai, J. H.
    et al.
    Song, Y.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Yang, R.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Influence of alloying elements Nb, Zr, Sn, and oxygen on structural stability and elastic properties of the Ti2448 alloy2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 1, s. 014103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanisms of how alloying elements and oxygen influence the stability and elastic properties of binary Ti-X (X = Nb, Zr, or Sn) and Ti2448 (Ti-24Nb-4Zr-8Sn in wt.%) alloys are studied via first principles calculations. In addition to the fully disordered solid solution phase, we consider 44 quasirandom configurations to search for the possible distributions of the alloying elements in Ti2448. Our results show that all alloying elements considered here are good β-stabilizers for Ti, and the formation energies are greatly affected by their distributions. The site preference of oxygen and its concentration dependence in binary Ti alloys and in Ti2448 are also investigated. Oxygen prefers to occupy the octahedral site regardless of the concentrations of the alloys and strongly interacts with Ti and Nb in Ti-Nb. The elastic properties of Ti2448 alloy and the influence of oxygen on the elastic parameters are evaluated. The calculated polycrystalline Young's modulus of the Ti2448 alloy is very close to that of the human bone (10-40 GPa). We find that oxygen has a weak effect on the elastic moduli of Ti2448. The electronic structures are analyzed to reveal how the alloying elements and oxygen influence the stability of binary Ti-X and Ti2448 alloys.

  • 4.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Chen, D.
    Long, M.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, H.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Computation of Phase Fractions in Austenite Transformation with the Dilation Curve for Various Cooling Regimens in Continuous Casting2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 3, s. 1553-1564Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A concise model is applied to compute the microstructure evolution of austenite transformation by using the dilation curve of continuously cast steels. The model is verified by thermodynamic calculations and microstructure examinations. When applying the model, the phase fractions and the corresponding transforming rates during austenite transformation are investigated at various cooling rates and chemical compositions. In addition, ab initio calculations are performed for paramagnetic body-centered-cubic Fe to understand the thermal expansion behavior of steels at an atomic scale. Results indicate that by increasing the cooling rate, the final volume fraction of ferrite/pearlite will gradually increase/decrease with a greater transforming rate of ferrite. The ferrite fraction increases after austenite transformation with lowering of the carbon content and increasing of the substitutional alloying fractions. In the austenite transformation, the thermal expansion coefficient is sequentially determined by the forming rate of ferrite and pearlite. According to the ab initio theoretical calculations for the single phase of ferrite, thermal expansion emerges from magnetic evolution and lattice vibration, the latter playing the dominant role. The theoretical predictions for volume and thermal expansion coefficient are in good agreement with the experimental data.

  • 5.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, D.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Long, M.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Longitudinal spin fluctuation contribution to thermal lattice expansion of paramagnetic Fe2017Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 95, nr 5, artikel-id 054426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using an efficient first-principles computational scheme for paramagnetic body-centered cubic (bcc) and face-centered cubic (fcc) Fe, we investigate the impact of thermal longitudinal spin fluctuations (LSFs) on the thermal lattice expansion. The equilibrium physical parameters are derived from the self-consistent Helmholtz free energy, in which the LSFs are considered within the adiabatic approximation and the anharmonic lattice vibration effect is included using the Debye-Grüneisen model taking into account the interplay between thermal, magnetic, and elastic degrees of freedom. Thermal LSFs are energetically more favorable in the fcc phase than in the bcc one giving a sizable contribution to the linear thermal expansion of γ-Fe. The present scheme leads to accurate temperature-dependent equilibrium Wigner-Seitz radius, bulk modulus, and Debye temperature within the stability fields of the two phases and demonstrates the importance of thermal spin fluctuations in paramagnetic Fe.

  • 6.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Dengfu
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Thermal spin fluctuation effect on the elastic constants of paramagnetic Fe from first principles2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 22, artikel-id 224420Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the impact of longitudinal thermal spin fluctuations on the temperature dependence of the elastic constants of paramagnetic body-centered-cubic (bcc) and face-centered-cubic (fcc) Fe. Based on a series of constrained local magnetic moment calculations, the spin fluctuation distribution is established using Boltzmann statistics and involving the Jacobian weight, and a temperature-dependent quadratic mean moment is introduced that accurately represents the spin fluctuation state as a function of temperature. We show that with increasing temperature, c' and c(44) for the fcc phase and c(44) for the bcc phase decrease at different rates due to different magnetoelastic coupling strengths. In contrast, c' in the bcc phase exhibits relatively high thermal stability. Longitudinal thermal spin fluctuations diminish the softening of both elastic constants in either phase and have comparatively large contributions in the fcc phase. In both bcc and fcc Fe, c(44) has a larger temperature factor than c'. On the other hand, c' is more sensitive to the longitudinal thermal spin fluctuations, which balance the volume-induced softening by 21.6% in fcc Fe.

  • 7.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermal spin fluctuations in CoCrFeMnNi high entropy alloy2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 12211Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High entropy alloys based on 3d transition metals display rich and promising magnetic characteristics for various high-technology applications. Understanding their behavior at finite temperature is, however, limited by the incomplete experimental data for single-phase alloys. Here we use first-principles alloy theory to investigate the magnetic structure of polymorphic CoCrFeMnNi in the paramagnetic state by accounting for the longitudinal spin fluctuations (LSFs) as a function of temperature. In both face-centered cubic (fcc) and hexagonal close-packed (hcp) structures, the LSFs induce sizable magnetic moments for Co, Cr and Ni. The impact of LSFs is demonstrated on the phase stability, stacking fault energy and the fcc-hcp interfacial energy. The hcp phase is energetically preferable to the fcc one at cryogenic temperatures, which results in negative stacking fault energy at these conditions. With increasing temperature, the stacking fault energy increases, suppressing the formation of stacking faults and nano-twins. Our predictions are consistent with recent experimental findings.

  • 8.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75121 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Plastic deformation modes in paramagnetic gamma-Fe from longitudinal spin fluctuation theory2018Ingår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 109, s. 43-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using an efficient first-principles computational scheme, we calculate the intrinsic stacking fault energy (gamma(isf) ) and the unstable stacking fault energy (gamma(usf)) of paramagnetic gamma-Fe as a function of temperature. The formation energies are derived from free energies accounting for thermal longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the accurate description of the temperature-dependent magnetism, intrinsic and unstable stacking fault energies, and have a comparatively large effect on gamma(isf) of gamma-Fe. Dominated by the magneto-volume coupling at thermal excitations, gamma(isf) of gamma-Fe exhibits a positive correlation with temperature, while gamma(usf )declines with increasing temperature. The predicted stacking fault energy of gamma-Fe is negative at static condition, crosses zero around 540 K, and reaches 71.0 mJ m(-2) at 1373 K, which is in good agreement with the experimental value. According to the plasticity theory formulated in terms of the intrinsic and unstable stacking fault energies, twinning remains a possible deformation mode even at elevated temperatures. Both the large positive temperature slope of gamma(usf) and the predicted high-temperature twinning are observed in the case of austenitic stainless steels.

  • 9.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Inst Solid State Phys & Opt, Wigner Res Ctr Phys, H-1525 Budapest, Hungary..
    Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 12576Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent developments of high-entropy alloys with high strength and high ductility draw attention to the metastability-engineering strategy. Using first-principle theory, here we demonstrate that reducing the Ta level in the refractory TiZrHfTax system destabilizes the body-centered cubic (bcc) phase and leads to the appearance of the hexagonal close-packed (hcp) phase embedded in the bcc matrix. The alloying-induced features of the elastic parameters for the cubic and hexagonal structures are mapped out in details, and strong sensitivity to the crystal lattice and chemistry is revealed. Results show softening of the bcc matrix with decreasing Ta concentration which ensures ductile behavior. However, the elastically nearly isotropic hcp precipitates possess enhanced resistance against shear which promotes strengthening of the TiZrHfTax dual-phase system. The present atomic-level insight provides strong evidence to the experimental observation, and emphasizes the significance of quantum-design for advanced multi-phase high-entropy alloys with excellent strength-ductility combinations.

  • 10.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary.;Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys2018Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, nr 6, artikel-id 064033Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.

  • 11.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Tian, Fuyang
    Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China..
    Shen, Jiang
    Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China..
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden.
    Temperature dependent stacking fault energy of FeCrCoNiMn high entropy alloy2015Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 108, s. 44-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stacking fault energy (SFE) of paramagnetic FeCrCoNiMn high entropy alloy is investigated as a function of temperature via ab initio calculations. We divide the SFE into three major contributions: chemical, magnetic and strain parts. Structural energies, local magnetic moments and elastic moduli are used to estimate the effect of temperature on each term. The present results explain the recently reported twinning observed below room-temperature and predict the occurrence of the hexagonal phase at cryogenic conditions.

  • 12.
    Li, Guijiang
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Delczeg-Czirjak, Erna K.
    Kvashnin, Yaroslav O.
    Eriksson, Olle
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy2014Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 26, s. 262405-Artikel i tidskrift (Refereegranskat)
    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.

  • 13.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles description of planar faults in metals and alloys2014Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Phase interface and stacking fault are two common planar defects in metallic materials. In the present thesis, the interfacial energy and the generalized stacking fault energy of random alloys are investigated using density functional theory formulated within the exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA).The interfacial energy is one of the key physical parameters controlling the formation of the Cr-richα’ phases during the phase decomposition in Fe-Cr ferrite stainless steels. This decomposition is believed to cause the so-called“475°C embrittlement”. Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475oC embrittlement. The effect of Al on the interfacial energy and the formation energy of Fe-Cr solid solutions are studied in this thesis. The interface between the decomposed Fe-rich α and Cr-rich α phases carries a positive excess energy, which represents a barrier for the process of phase separation. Our results show that for the α-Fe70Cr20Al10/α0-Fe100−x−yCryAlx(0≤x≤10, 55≤y≤80) interface, the Al content(x) barely changes the interfacial energy. However, when Al is partitioned only in the alpha phase, i.e. for the α-Fe100−x−yCryAlx/α0-Fe10Cr90(0≤x≤10,0≤y≤25) interface, the interfacial energy increases with Al concentration due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. The intrinsic energy barriers (IEBs) of the γ surface (also called generalized stacking fault energy, GSFE) provide fundamental physics for understanding the plastic deformation mechanisms in face-centred cubic metals and alloys. In this thesis, the GSFEs of the disordered Cu-X (X=Al, Zn, Ga, Ni) and Pd-X (X=Ag,Au) alloys are calculated. Studying the effect of segregation of the solutes to the stacking fault planes shows that only the local chemical composition affects the GSFEs. Based on the calculated GSFEs values, the previously revealed “universal scaling law” between these IEBs is demonstrated to be well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability. Our theoretical predictions are in line with the available experimental data. These achievements open new possibilities in understanding and describing the plasticity of complex alloys.

  • 14.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles description of planarfaults in metals and alloys2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Phase interface and stacking fault are two common planar defects in metallic materials. In the present thesis, the interfacial energy and the generalized stacking fault energy of random alloys are investigated using density functional theory formulated within the exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA).

    The interfacial energy is one of the key physical parameters controlling the formation of the Cr-richα’ phases during the phase decomposition in Fe-Cr ferrite stainless steels. This decomposition is believed to cause the so-called “475°Cembrittlement”. Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475oC embrittlement. The effect of Al on the interfacial energy and the formation energy of Fe-Cr solid solutions are studied in this thesis. The interface between the decomposed Fe-rich α and Cr-richα0 phases carries a positive excess energy, which represents a barrier for the process of phase separation. Our results show that for the α-Fe70Cr20Al100-Fe100−x−yCryAlx (0≤x≤10, 55≤y≤80) interface, the Al con-tent(x) barely changes the interfacial energy. However, when Al is partitioned only in the alpha phase, i.e. for the α-Fe100−x−yCryAlx0-Fe10Cr90 (0≤x≤10, 0≤y≤25) interface, the interfacial energy increases with Al concentration due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying.

    The intrinsic energy barriers (IEBs) on theγ−surface (also called generalized stacking fault energy, GSFE) provide fundamental physics for understanding the plastic deformation mechanisms in face-centred cubic (fcc) metals and alloys. In this thesis, the GSFEs of the disordered Cu-X (X=Al, Zn, Ga, Ni) and Pd-X (X=Ag, Au) alloys are calculated. Studying the effect of segregation of the solutes to the stacking fault planes shows that only the local chemical composition affects the GSFEs. Based on the calculated GSFE values, the previously revealed “universal scaling law” between these IEBs is demonstrated to be well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, the addition of Al, Zn and Ga increases the twinnability, while adding Ni decreases it. Aluminum and gallium yield similar effects on the twinnability. Our theoretical predictions are in line with the available experimental data. These achievements open new possibilities in understanding and describing the plasticity of complex alloys.

    We investigate theγ-surface of paramagneticγ-Fe as a function of temperature. At ambient conditions, the fcc lattice is thermodynamically unstable with respect to the hexagonal close-packed (hcp) lattice, resulting in negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along theγ-surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recently developed plasticity theory, the overall effect of temperature is to move the plastic deformation mode of the paramagnetic fcc Fe from the stacking fault formation regime (T <<300K) towards maximum twinning (T≈300K) and finally to a dominating full-slip regime (T >>300K). Our predictions are discussed in connection with the available experimental observations.

    The same methodology is used to establish theγ-surface of Fe-Cr-Ni alloys as a function of chemical composition and temperature. We fix the concentration of Cr at 20 at.%. Nickel is found to increase the intrinsic stacking fault (SFE), unstable stacking fault (USF) and unstable twin fault (UTF) energies. The theoretical SFE versus chemistry and temperature trends agree well with experiments. Both USF and UTF decrease with increasing temperature. The calculated IEBs are used to establish the temperature and composition dependence of the deformation modes in Fe-Cr-Ni alloys. Stacking fault formation is predicted to be the leading deformation mechanism for alloys with effective SFE below∼18mJm−2, which is in good agreement with the observed upper limit of the SFE for the TRIP (transformation-induced plasticity) mechanism. Alloys with SFE above this critical value show both twinning and full slip at room temperature and surprisingly, even the SFE is very high, twinning remains a possible deformation mode even at elevated temperatures, which is in line with observations

  • 15.
    Li, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Grehk, Mikael
    Johnsson, Jan Y.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Generalized stacking fault energy of γ-FeManuskript (preprint) (Övrigt vetenskapligt)
  • 16.
    Li, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    Kwon, Se Kyun
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Generalized stacking fault energies of alloys2014Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, nr 26, s. 265005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The generalized stacking fault energy (gamma surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the. surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the. surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys. Based on our. surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.

  • 17.
    Li, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hu, Qing-Miao
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    The effect of Al on the 475 degrees C embrittlement of Fe-Cr alloys2013Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 74, s. 101-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475 degrees C embrittlement resulting from the phase decomposition in concentrated Fe-Cr alloys. With the aim of revealing the mechanism behind this prosperous phenomenon, here we investigate the effect of Al on the interfacial energy and formation energy of Fe-Cr solid solutions. The interface between the decomposed Fe-rich alpha and Cr-rich alpha' phases carries a positive excess energy, which is of significant importance on determining the process of phase separation. Using ab initio alloy theory, we show that for the alpha-Fe70Cr20Al10/alpha'-Fe100-x-yCryAlx (0 <= x <= 10, 55 <= y <= 80) interface, the Al content (x) barely changes the interfacial energy. However, for the alpha-Fe100-x-yCryAlx/alpha'-Fe10Cr90 (0 <= x <= 10, 0 <= y <= 25) interface, the interfacial energy increases with Al content due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. Our ab initio results are supported by CALPHAD calculations, and suggest that the beneficial effect of Al on ferritic steels is mainly due to its thermodynamical effect on the alpha' phase.

  • 18.
    Li, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, University of Turku, Turku, Finland.
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, Kalevi
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hertzman, Staffan
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Division of Materials Theory, Uppsala University, Sweden.
    First-principles prediction of the deformation modes in austenitic Fe-Cr-Ni alloys2016Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, nr 8, artikel-id 081903Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles alloy theory is used to establish the gamma-surface of Fe-Cr-Ni alloys as function of chemical composition and temperature. The theoretical stacking fault energy (SFE) versus chemistry and temperature trends agree well with experiments. Combining our results with the recent plasticity theory based on the gamma-surface, the stacking fault formation is predicted to be the leading deformation mechanism for alloys with effective stacking fault energy below similar to 18 mJ m(-2). Alloys with SFE above this critical value show both twinning and full slip at room temperature. Interestingly, twinning remains a possible deformation mode in addition to full slip even at elevated temperatures, in line with observations.

  • 19.
    Li, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kokko, Kalevi
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kwon, Se Kyun
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-Principles prediction of the deformation modes in austenitic Fe-Cr-Ni alloysManuskript (preprint) (Övrigt vetenskapligt)
  • 20.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhang, Hualei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Jijun
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Elastic properties of vanadium-based alloys from first-principles theory2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 1, s. 014105-Artikel i tidskrift (Refereegranskat)
    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.

  • 21. Lu, Jun
    et al.
    Hultman, Lars
    Holmstrom, Erik
    Antonsson, Karin H.
    Grehk, Mikael
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Golpayegani, Ardeshir
    Stacking Fault Energies in austenitic stainless steelsManuskript (preprint) (Övrigt vetenskapligt)
  • 22.
    Molnár, Dávid Sándor
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Materials Science Group, Dalarna University, Falun, SE-791 88, Sweden.
    Engberg, G.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Uppsala, SE-75120, Sweden; Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Budapest, H-1525, Hungary.
    Deformation properties of austenitic stainless steels with different stacking fault energies2018Ingår i: Mater. Sci. Forum, Trans Tech Publications Ltd , 2018, s. 190-197Konferensbidrag (Refereegranskat)
    Abstract [en]

    In FCC metals a single parameter – stacking fault energy (SFE) – can help to predict the expectable way of deformation such as martensitic deformation, deformation twinning or pure dislocation glide. At low SFE one can expect the perfect dislocations to dissociate into partial dislocations, but at high SFE this separation is more restricted. The role of the magnitude of the stacking fault energy on the deformation microstructures and tensile behaviour of different austenitic steels have been investigated using uniaxial tensile testing and electron backscatter diffraction (EBSD). The SFE was determined by using quantum mechanical first-principles approach. By using plasticity models we make an attempt to explain and interpret the different strain hardening behaviour of stainless steels with different stacking fault energies. 

  • 23.
    Molnár, Dávid Sándor
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Materials Science Group, Dalarna University, Falun, SE-791 88, Sweden.
    Engberg, Göran
    Högskolan Dalarna.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hedström, Peter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kwon, Se Kyun
    Pohang University of Science and Technology.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Experimental study of the γ-surface of austenitic stainless steels2019Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, s. 34-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

  • 24.
    Molnár, Dávid Sándor
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Högskolan Dalarna.
    Sun, Xun
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Engberg, Göran
    Högskolan Dalarna.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, s. 490-497Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

  • 25.
    Xie, Ruiwen
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Song, Yan
    Harbin Inst Technol Weihai, Sch Mat Sci & Engn, Weihai 264209, Peoples R China..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Uppsala, Sweden.;Inst Solid State Phys & Opt, Wigner Res Ctr Phys, Budapest, Hungary..
    Generalized stacking fault energy of carbon-alloyed paramagnetic gamma-Fe2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 6, artikel-id 065703Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Generalized stacking fault energy (GSFE) is an important parameter for understanding the underlying physics governing the deformation mechanisms in face-centred cubic (fcc) materials. In the present work, we study the long-standing question regarding the influence of C on the GSFE in austenitic steels at paramagnetic state. We calculate the GSFE in both gamma-Fe and Fe-C alloys using the exact muffin-tin orbitals method and the Vienna Ab initio Simulation Package. Our results show that the GSFE is increased by the presence of interstitial C, and the universal scaling law is used to verify the accuracy of the obtained stacking fault energies. The C-driven change of the GSFE is discussed considering the magnetic contributions. The effective energy barriers for stacking fault, twinning and slip formation are employed to disclose the C effect on the deformation modes, and we also demonstrate that the magnetic structures as a function of volume explain the effect of paramagnetism on the C-driven changes of the stacking fault energies as compared to the hypothetical non-magnetic case.

  • 26.
    Xie, Ruiwen
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lizárraga, Raquel
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Linder, David
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hou, Ziyong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Lattemann, M.
    Holmström, E.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Quantum mechanics basis of quality control in hard metals2019Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 169, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-destructive and reliable quality control methods are a key aspect to designing, developing and manufacturing new materials for industrial applications and new technologies. The measurement of the magnetic saturation is one of such methods and it is conventionally employed in the cemented carbides industry. We present a general quantum mechanics based relation between the magnetic saturation and the components of the binder phase of cemented carbides, which can be directly employed as a quality control. To illustrate our results, we calculate the magnetic saturation of a binder phase, 85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical predictions to the magnetic saturation measurements. We also analyse interface and segregation effects on the magnetic saturation by studying the electronic structure of the binder phase. The excellent agreement between calculations and measurements demonstrates the applicability of our method to any binder phase. Since the magnetic saturation is employed to ensure the quality of cemented carbides, the present method allows us to explore new materials for alternative binder phases efficiently.

  • 27. Zhao, W.
    et al.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gong, S.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sun, Z.
    Thermo-mechanical properties of Ni-Mo solid solutions: A first-principles study2019Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 158, s. 140-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical strength of Ni-based single-crystal superalloys under service condition is related to the thermo-mechanical properties of the disordered γ matrix. Here we use density functional theory and quasi-harmonic approximation to determine the temperature-dependent bulk moduli and generalized stacking fault energies (GSFEs) of Ni-Mo solid solutions. We show that the increasing temperatures between 1000 K and 1400 K cause evident reductions in the bulk moduli and planar fault energies of Ni-Mo alloys. Furthermore, their negative slopes versus temperature are gradually diminished with increasing Mo concentration except that of the unstable stacking fault energy. Adopting recent theoretical models for twinning based on GSFE, increasing temperature enhances the twinnability of low-Mo alloys but has limited influences in the case of high-Mo alloys. The composition-dependent thermal expansion, the thermal electronic excitation and the magnetic transition are shown to be the main factors rendering the complex variations in the elastic properties and twinning behavior of Ni-Mo solid solution with temperature.

  • 28.
    Zhao, Wenyue
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sun, Z.
    Gong, S.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Tuning the plasticity of Ni-Mo solid solution in Ni-based superalloys by ab initio calculations2017Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 124, s. 100-107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The generalized stacking fault energies of face centered cubic Ni-Mo solid solutions are calculated using the exact muffin-tin orbital method in combination with coherent potential approximation. The alloying of Mo in Ni is found to decrease the intrinsic stacking fault energy of the solid solution from 150 mJ/m2 (pure Ni) to 50 mJ/m2 (17.5 at.% Mo) almost linearly. At the same time, the unstable stacking fault energy (the unstable twin fault energy) of the Ni-based solid solution increases (decreases) in a small extent with increasing Mo concentration. Three different twinnability measures are adopted and all indicate a substantially enhanced twinning mechanism in Ni-Mo solid solutions with increasing concentration of Mo. The weaker Ni-Ni bonding at high Mo concentrations is considered to be the main mechanism behind the disclosed phenomena. Segregation of Mo to the fault plane is proved to have strong effect on the generalized stacking fault energy of Ni-based solid solution.

1 - 28 av 28
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