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The substitutional solute atom induced local lattice distortion (LLD) in dilute metal solid solution was believed to be uniform because the solute atom was supposed to occupy the high symmetry lattice site without breaking the point group symmetry of the crystal lattice. Contrary to this conventional picture, we report in this paper that substitutional Mo atom in Ti-Mo solid solution occupies an off-center position instead of the high symmetry lattice site and leads to highly non-uniform LLD, as evidenced by our first principles calculations. The physics underlying the off-center occupation and non-uniform LLD are shown to be the Jahn-Teller splitting of the degenerated d states of Mo atom. With which, the solid-solutions suffering from non-uniform LLD are predicted. The non-uniform LLD challenges the application of classical solid solution hardening model based on uniform LLD and spherical stress tensor assumption to this kind of solid solutions. This work also questions the traditional view that elementary substitutional solute atoms in metal solid solutions should not induce anelastic relaxation and internal friction. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this paper, an effective and low-cost way of Na-incorporation was used for grain-growth promotion in CIGSe films. If the CIGSe film was selenized with SLG as both substrate and cover, large-grained CIGSe film without fine grains was obtained. The PCE of corresponding CIGSe solar cell showed highest PCE of 11.5%, which is quite higher than our previous reported 9.5%. • Element precursor solution method was used to fabricate CIGSe solar cells. • The SLG cover was used as Na-incorporation way for grain-growth. • The SLG cover is beneficial for impure CISe phase elimination. • The SLG cover can promote the crystal growth of CIGSe film. • The fabricated CIGSe solar cells showed highest PCE of 11.5%. Cu(In,Ga)Se 2 (CIGSe) based solar cells have received considerable interests because they have reached the commercialization stage. High efficiency CIGSe based solar cells are often fabricated via post deposition treatment (PDT) with alkali metal element incorporation. In this work, we present an effective and low-cost way of Na-incorporation for photoelectric conversion efficiencies (PCE) promotion of CIGSe solar cells. Soda-lime glass (SLG) was used as both substrate and cover during the PDT procedure for Na doping. The effects of different substrate and cover on the grain size and phase composition of CIGSe films were studied in detail. The Na- incorporation from SLG significantly improved the grain growth, charge carrier density and V oc of CIGSe solar cells. At last, a best 11.53% PCE CIGSe solar cell was achieved at optimal condition. [ABSTRACT FROM AUTHOR]

In the present work, a first-principles method is used to calculate the oxidation energies of Al 2 O 3 and TiO 2 as well as the formation energy of oxygen vacancy in TiO 2 containing various alloying elements, in order to shed some light on the alloying effects on the oxidation resistance of γ -TiAl. Our calculations demonstrate that almost all alloying elements increase the oxidation energies of Al 2 O 3 and TiO 2 . The alloying elements with number of d electrons from 2 to 5 in the forth and fifth rows of the periodic table (e.g., Zr, Nb, Mo, Hf, Ta, W) increase significantly the oxidation energy difference between Al 2 O 3 and TiO 2 , i.e., reduce the relative stability of Al 2 O 3 to TiO 2 . On the other hand, these alloying elements increase the formation energy of oxygen vacancy in TiO 2 . The effects of other alloying elements are less significant or opposite. Observing the experimental mass gains of TiAl alloys and unalloyed TiAl due to oxidation, we find that the elements reducing the relative stability of Al 2 O 3 to TiO 2 and increasing the formation energy of oxygen vacancy enhance the oxidation resistance of TiAl whereas others do not. Such correlations are rationalized by analyzing the alloying effects on the internal oxidation of Al in the γ -TiAl matrix and the diffusion of oxygen in TiO 2 surface scale. [ABSTRACT FROM AUTHOR]

Abstract: Stacking fault energy (SFE) plays an important role in the plastic deformation of metals. As compared to those of face-centered cubic metals, the SFEs of hexagonal close-packed (hcp) metals are less reported in literature. In this paper, we derive the expressions of four types (I 1, I 2, E and T 2) of basal plane SFEs of hcp metals in terms of the interlayer interaction energies within the framework of the Ising model. The SFEs of 14 kinds of hcp metals are then evaluated with the interlayer interaction energies extracted from the total energies of four prototypes calculated by using the first-principles full-potential augmented plane-wave method. We show that the hcp metals can be divided into three types according to their interlayer interaction energies. For all the hcp metals involved in this study, I 1 has the lowest SFE, whereas E has the highest. The metals (Mg, Co, Zn and Cd) with principal slip system (0001) generally have low basal plane SFEs. The I 1 and T 2 SFEs increase linearly with the energy difference between double hexagonal close-packed and hcp structures, whereas the I 2 and E SFEs increase linearly with the energy difference between the short-period twin and hcp structures, indicating a trivial contribution of the interaction energy between atomic layers over third nearest neighbors to the SFEs. The SFEs also correlate with the cohesive energy density (cohesive energy of unit volume) with the exception of Be, Co, Tc and Re. [Copyright &y& Elsevier]

Abstract: Although the stacking fault energy (SFE) is a fundamental variable determining the minimum grain size (d min) obtainable in severe plastic deformation (SPD) processes, its accurate measurement is difficult. Here we establish the SFEs of binary Pd–Ag, Pd–Cu, Pt–Cu and Ni–Cu solid solutions using the axial interaction model and the supercell model in combination with first-principles theory. The two models yield consistent formation energies. For Pd–Ag, Pd–Cu and Ni–Cu, the theoretical SFEs agree well with those from the experimental measurements. For Pt–Cu no experimental results are available, and thus our calculated SFEs represent the first reasonable predictions. We discuss the correlation of the SFE and d min in SPD experiments and show that the d min values can be evaluated from first-principles calculations. [Copyright &y& Elsevier]

Abstract: The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of austenitic stainless steels, Fe–Cr–Ni with various Ni contents, are investigated via quantum–mechanical first-principles calculations. In the composition range (c Cr =20%, 8⩽ c Ni ⩽20%, 0⩽ c Mn, c Co, c Nb ⩽8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0K but increases it at room temperature in high-Ni (c Ni ≳16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe–Cr–Ni alloys is inverted to an SFE-decreasing effect by Nb for c Nb ≳3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE. [Copyright &y& Elsevier]

Abstract: The origin of the superior high temperature strength of Ti-rich γ-TiAl with addition of Nb is a highly controversial issue. In this paper, we calculated the interaction energies between point defects in these alloys using a first-principles plane-wave pseudopotential method. It is found that, the nearest neighbouring Nb atoms on Al-sublattice (NbAl) repel whereas the next nearest neighbouring NbAl atoms attract each other, indicating that NbAl atoms may form short-range ordered structure. Based on this finding, we propose that the short-range order may be responsible for the high strength of the Ti-rich TiAl-Nb alloys. [Copyright &y& Elsevier]

Abstract: The composition-dependent elastic properties and electronic structure of off-stoichiometric TiNi with a B2 structure are investigated by using the first-principles exact muffin-tin orbitals method in combination with coherent potential approximation and first-principles plane-wave pseudopotential method (for computing bonding charge densities). The Zener anisotropy, c 44/c′, increases with increasing Ni contents, but is quite small, indicating a strong correlation between the softening of c 44 and c′ with decreasing temperature during martensitic transformation (MT). For the Ni-rich TiNi, c 44 increases with increasing Ni content whereas c′ decreases. On the Ti-rich side, both c 44 and c′ are insensitive to the composition. It was observed that larger c 44 corresponds to higher MT temperature, and the composition dependence of elastic modulus is discussed on the basis of the bonding charge densities and electronic density of states. We propose that the strong composition dependence of the elastic modulus of the Ni-rich TiNi can be attributed to the Coulomb static electronic repulsion between the antisite Ni atoms and their surroundings. The insensitivity of the elastic modulus of the Ti-rich TiNi to the composition is due to the absence of such repulsion between the Ti antisites and their nearest neighbors. [Copyright &y& Elsevier]

Abstract: The Ising-like phase transition of two-dimensional fully frustrated XY (FFXY) model with time dependent Ginzburg–Landau (TDGL) dynamics is studied by using the short-time dynamics scaling analysis. The transition temperature and the dynamic and static critical exponents z, , and ν are estimated and are compared with the results of FFXY model under resistively-shunted junction dynamics (RSJ) and Monte Carlo (MC) dynamics. We find , z, and ν are roughly independent of dynamic mode but is dependent on the dynamic mode. [Copyright &y& Elsevier]

Abstract: First-principles method based on the electronic structure theory is one of the most promising approaches of computational materials design. Although only a few of mechanical properties (e.g., ideal strength and elastic constants) are accessible directly by first-principles calculations, such methods may predict the complex mechanical properties by extracting appropriate calculable parameters (e.g., the ratio of bulk modulus to shear modulus, the formation energies of and interaction energies between lattice defects) and adopting proper models (e.g., Peierls–Nabarro model for dislocation core). In this paper, we briefly review recent first-principles investigations of mechanical properties of structural materials, covering topics of ideal strength, elastic constants, and lattice defects. Some of the major recent advances, such as the application of coherent potential approximation coupled first-principles methods (accurate enough for the calculating of the elastic constants of random alloys with complex compositions), the appreciation of the importance of low C 11–C 12 to the ‘super properties’ of BCC-Ti based alloys, and the relationship between solute–vacancy interaction and creep resistance, etc., are highlighted. [Copyright &y& Elsevier]

During an investigation of mycoparasitic fungi on sclerotia of Sclerotinia sclerotiorum in China, a new fungal species was consistently encountered and isolated from natural soils taken from soybean fields of Shandong and Jiangsu Provinces. The fungus is featured by its sphaeroid conidia with 1–2 transverse septa, but mostly (>65%) with only one septum at the base. It resembles Monacrosporium indicum, M. sphaeroides and M. sinense, but can be distinguished from the first two species by lack of basal hila and large vacuoles on its conidia, respectively, and from M. sinense by its typically two-celled and broadly turbinate to napiform conidia. Colonization frequencies on S. sclerotiorum sclerotia by the new species were 10% and 33.3% in the two field soils, respectively, when the sclerotia were introduced into soils and coincubated at 22–24 °C for 4 wk. Reinoculation tests by placing surface-sterilized sclerotia onto the tested isolate colony for 2 wk and then surface-sterilized again resulted in 23.3% sclerotia colonized. Microscopic observations indicated that the fungus coiled around hyphae of Rhizoctonia solani and grew along and appressed to hyphae of Fusarium solani f.sp. pisi, S. sclerotiorum and Phytophthora cactorum when dual-cultured in slides. Tests on agar plates demonstrated that the fungus formed adhesive networks and was an active predator of Panagrellus redivivus. This study indicated the diverse mechanisms for the fungus to survive in soil. For expression of its mycoparasitic and nematode-trapping capacities, the fungus is named as Monacrosporium janus. [ABSTRACT FROM AUTHOR]

Solute atoms such as Fe, Co, and Ni diffuse abnormally fast in α -Ti, which influences significantly the mechanical properties of the titanium alloys. Various mechanisms (e.g., the interstitial diffusion mechanism and solute-vacancy complex mechanism) have been proposed to account for the fast diffusion of these solutes in α -Ti. To elucidate such diffusion mechanism, a first-principles method is employed to calculate the formation energies, migration energy barriers, and solute-vacancy binding energies of the substitutional and interstitial solute atoms including Al, Si, Sn, V, Mn, Fe, Co, Ni, and Cu in α -Ti. Based on the calculated parameters, the diffusion mechanisms are discussed. Comparing the formation energies of the substitutional and interstitial solutes, we find that all the solute atoms prefer the substitutional configuration to the interstitial one. The interstitial migration energy barriers are quite low for all the solutes. Al and Sn diffuse mainly through normal vacancy mediated mechanism due to the high substitutional to interstitial preferential energy that leads to very low fraction of interstitial solutes (about 10 − 15 ∼ 10 − 16 at 1000 K) at thermal equilibrium state and high interstitial diffusion activation energy. The 3d metal solute atoms, especially Mn, Fe, and Co, are fast diffusers and the diffusion coefficients are dominated by the interstitial mechanism because of their sizable thermal equilibrium interstitial fractions (several percent at 1000 K). The solute-vacancy complex mechanism is not likely to account for the fast diffusions in α -Ti. We show that the direct chemical interaction between the solute and matrix atoms determines the site-occupancy of the solute atoms in α -Ti besides the atomic size effect that was commonly believed to be responsible for the fast diffusions. [ABSTRACT FROM AUTHOR]

Breakdown of Schmid's law is a long-standing problem for exploring the orientation-dependent deformation mechanism in intermetallics. The lack of atomic-level understanding of the selection rules for the plastic deformation modes has seriously limited designing strong and ductile intermetallics for high-temperature applications. Here we put forward a transparent model solely based on first principles simulations for mapping the deformation modes in γ -TiAl polysynthetic twinned alloys. The model bridges intrinsic energy barriers and different deformation mechanisms and beautifully resolves the complexity of the observed orientation-dependent deformation mechanisms. Using the model, one can elegantly reveal the atomic-level mechanisms behind the unique channeled flow phenomenon in lamellar TiAl alloys. [ABSTRACT FROM AUTHOR]

The lattice constant, formation enthalpy, and elastic parameters of Cu 1 - x Au x (0 ⩽ x ⩽ 1) alloys in the face centered cubic crystallographic phase are investigated by using the first-principles exact muffin-tin orbitals and plane-wave pseudopotential methods in order to explore the effect of alloying with special focus on the impact of local lattice distortion (LLD) on the above properties. The compositional disorder is treated within the framework of the coherent potential approximation (CPA) and the special quasi-random structure (SQS) scheme. Calculations based on SQS and CPA show that, while LLD lowers significantly the formation enthalpy of Cu 1 - x Au x due to the large size mismatch between Cu and Au atoms, it has negligible influence on the lattice constants and elastic parameters. These findings confirm the reliability of CPA for computing the enthalpy changes upon isotropic and unisotropic lattice distortions in disordered alloys with sizable atomic size differences. [ABSTRACT FROM AUTHOR]

First-principles method is used to characterize segregation and magnetic properties of alloyed Ti/TiO 2 interface. We calculate the segregation energy of the doped Ti/TiO 2 interface to investigate alloying atom's distribution. The oxidation resistance of Ti/TiO 2 interface is enhanced by elements Fe and Ni but reduced by element Co. Magnetism could be produced by alloying elements such as Co, Fe and Ni in the bulk of titanium and the surface of Ti at Ti/TiO 2 interface. The presence of these alloying elements could transform the non-magnetic titanium alloys into magnetic systems. We have also calculated the temperature dependence of magnetic permeability for the doped and pure Ti/TiO 2 interfaces. Alloying effects on the Curie temperature of the Ti/TiO 2 interface have been elaborated. [ABSTRACT FROM AUTHOR]

Hydride induced embrittlement is one of the main causes for the stress corrosion crack of titanium alloys. The formation process of the hydride at atomic level remains controversial as it is not accessible directly by experiments. In the present work, the formation of titanium hydride is investigated by using a first principles method. By calculating the formation energies of TiH m with various types of H occupation state in HCP and FCC Ti matrix, we show that there exists phase equilibrium between α-Ti-H solid solution and δ/ε hydrides with χ and γ hydrides appearing as metastable phases. The energy barrier for the HCP → FCC structure transformation for the formation of the hydrides decreases with increasing H:Ti ratio m. The structure transformation is accompanied with spontaneous shift of half amounts of the H atoms from the octahedral to the tetrahedral interstices. The energy barrier for the migration of the remaining half of the H atoms from the octahedral to the tetrahedral interstices reduces with increasing m and approaches to a constant value. The hydrostatic compressive stress acting on TiH m , resulted from the H-induced lattice dilation tendency and the constraint of the surrounding matrix, does not facilitate the HCP → FCC transformation and the migration of the H atoms. The present work sheds light on the hydride formation process at atomic level. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the effect of Al on the interfacial and formation energy of Fe–Cr alloys. [•] Al rarely change the interfacial energy between the α and α′ phases. [•] Al suppresses the phase separation of Fe–Cr alloys by destabilizing the α′ phase. [•] The α + α′ phase boundary is shifted to high Cr content by Al. [Copyright &y& Elsevier]

Abstract: The crystallographic structure and stability of the phase relative to the and phases in Ti–x M (M=Ta, Nb, V, Mo) alloys are investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. We show that, with increasing concentration of the alloying elements, the structure of the orthorhombic- phase evolutes from the hcp- to the bcc- phase, i.e., the lattice parameters b/a and c/a as well as the basal shuffle y decreases from those corresponding to the phase to those of the phase. The compositional and phase boundaries are determined by comparing the total energies of the phases. The predicted phase boundaries are about 10.2, 10.5, 11.5, 4.5at% for Ti–V, Ti–Nb, Ti–Ta, and Ti–Mo, respectively, in reasonable agreement with experiments. The phase boundaries are higher than the experimental values, possibly due to the absence of temperature effect in the first-principles calculations. Analyzing the electronic density of states, we propose that the stability of the phase is controlled by the compromise between the strength of the covalent and metallic bonds. [Copyright &y& Elsevier]

We report a comprehensive study on the structure and elastic constants of epitaxial cubic δ-Ta x N (x ≈ 1) layers deposited by reactive magnetron sputtering at 570 °C on MgO(001), MgO(110) and MgO(111) substrates. X-ray diffraction shows that all layers are single-phase and have a single-crystal rocksalt-structure, growing with an epitaxial cube-on-cube relationship with respect to their MgO substrates. For (001)-orientation, Brillouin light scattering provides the measurement of c 44 (137 ± 3 GPa) and c 12 (130 ± 5 GPa) single-crystal elastic constants, while picosecond laser ultrasonics (PLU) provides the third independent one, c 11 (530 ± 10 GPa). For (110)- and (111)-orientations, PLU provides selectively the following combinations, (c 11 +c 12 +2c 44)/2 and (c 11 +2c 12 +4c 44)/3, respectively. Electrical resistivity measurements show evidence of point defects in the films despite a composition close to 1:1 stoichiometry. Point defects (metal and nitrogen vacancies) are considered in our first-principles calculations to find closer agreement between experimental and theoretical lattice parameter, mass density, sound velocities and elastic constants. Sound velocities and elastic constants are found to be particularly sensitive to the presence of vacancies, resulting into a more compliant and less anisotropic material. While only ∼ − 1% mismatch is found between predicted defect-free and experimental lattice parameters, huge differences of −27% and +180% are observed for c 11 and c 44 , respectively. These discrepancies can be rationalized by considering the presence of point defects (metal vacancy and/or Schottky defect) in concentration ∼11% in the as-deposited TaN films, a compositional value that corresponds to the lowest formation energy of δ-TaN x structure. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The present work systematically clarifies the influence of the atomic mixing and the atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal) on the molar volume of the binary sigma phase. We calculated the molar volumes of 21 binary sigma compounds with different atomic order by using EMTO-CPA (Exact Muffin-Tin Orbitals - Coherent Potential Approximation) method. The calculation results follow a similar trend as the experimental data. Moreover, the calculated molar volumes with respect to the composition of the sigma phase in disordered states show that the sigma compounds do not comply with the linear volume-composition relationship. This is due to the influence of the atomic mixing and the deviation can be either negative or positive depending on the tendency of electron loss or gain of the two constituent elements. Additionally, we compared the molar volume difference (ΔVm = V disorder -V order ) between the hypothetically disordered and ordered states of the binary sigma compounds. The results indicate that the effect of the atomic order on the molar volume of the sigma phase depends on the size difference and the electron configurations of the two constituent elements. [ABSTRACT FROM AUTHOR]

[3+2] reactions play a key role in constructing various pharmaceutical moleculars. In this study, using Mn(OAc) 3 mediated and 1,3-dipolar [3+2] cyclization reactions, 38 novel dihydrofuran and dihydroisoxazole analogues of iso CA-4 were synthesized as inhibitors of tubulin polymerization. Among them, compound 6g was found to be the most potent cytotoxic agents against PC-3 cells with IC 50 value of 0.47 μM, and compound 5p exhibted highest activity on HeLa cells with IC 50 vaule of 2.32 µM. Tubulin polymerization assay revealed that 6g was a dose-dependent and effective inhibitor of tubulin assembly. Immunohistochemistry studies and cell cycle distribution analysis indicated that 6g severely disrupted microtubule network and significantly arrested most cells in the G2/M phase of the cell cycle in PC-3 cells. In addition, molecular docking studies showed that two chiral isomers of 6g can bind efficiently and similarly at colchicine binding site of tubulin. [ABSTRACT FROM AUTHOR]

In this work, site-preference and elastic properties of TiNi-Nb austenite were investigated for various compositions, by using Exact Muffin-Tin Orbitals method in conjunction with Coherent Potential Approximation (EMTO-CPA). Moreover, composition-dependent elastic constants were calculated and used to explain the relation between composition and martensitic transition temperature. Our calculations suggested that Nb atoms prefer to occupy either Ni sites or Ti sites, depending strongly on composition. Variation of TiNi-Nb compositions is achieved through the formation of four sorts of defects: substituting Ti by Nb, substituting Ni by Nb, Ti anti-sites and Ni anti-sites. Our results suggested that c ′increases when Ni is substituted by Nb, while c 44 increases when Ni is substituted by Nb or Ni anti-sites form. Moreover, the maps of composition-dependent elastic constants were presented. TiNi-Nb with high c ′and c 44 could be obtained in Ni-deficient area. However, in Ni-excess area, only high c 44 could be obtained. Changing of martensitic transition temperature is sensitive to the variation of c 44 , rather than c ′. With the variation of c 44 , we explained the composition-dependent martensitic transition temperature for TiNi-Nb. [ABSTRACT FROM AUTHOR]

A plane wave pseudo-potential method based on density functional theory is employed to calculate the migration energy barrier for the atomic self-diffusion in HCP metals including Mg, Zn, Ti, Zr, and Hf. The influences of some key factors (plane-wave cutoff energy, k -mesh, supercell size, and geometric optimization scheme) on the calculated migration energy barrier and its anisotropy are systematically investigated. We show that the supercell size affects heavily the migration energy barrier and its anisotropy for the metals with valence d electrons (Ti, Zr, and Hf) but not for the ones with only valence s metals (Mg). In general, the anisotropy of the migration energy barrier reduces with increasing size of the supercell especially for Ti, Zr, and Hf. The optimization of the shape and volume of the supercell matters for the migration energy barrier calculated with the small size supercell but not for that calculated with the large supercell. With the calculated migration energy barrier, the self-diffusion coefficients are evaluated based on the transition state theory and compared with other first-principles calculations and the experimental measurements. [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed to study the effect of C on the stacking fault energy (SFE) of paramagnetic γ -Fe and Fe Cr Ni austenitic steel. In these systems, the local magnetic structure is very sensitive to the volume in both fcc and hcp structures, which emphasizes the importance of the magnetovolume coupling effect on the SFE. The presence of C atom suppresses the local magnetic moments of Fe atoms in the first coordination shell of C. Compared to the hypothetical nonmagnetic case, paramagnetism significantly reduces the effect of C on the SFE. In the scenario of C being depleted from the stacking fault structure or twin boundaries, e.g. , due to elevated temperature, where the chemical effect of C is dissipated, we calculate the C-induced volume expansion effect on the SFE. The volume induced change in the SFE corresponds to more than ∼ 50% of the total C effect on the SFE obtained assuming uniform C distribution. [ABSTRACT FROM AUTHOR]

The phase stability and elastic property of binary Ti- x TM (TM = V, Cr, Nb, Mo) and ternary Ti-15TM- y Al alloys are investigated systematically by using a first-principles method. The coherent potential approximation is employed to describe the random distribution of the alloying atoms in the alloys. We show that the transition metal (TM) elements V, Cr, Nb, Mo increase the elastic stability of the β phase but decreases that of the α phase. The polycrystalline bulk modulus of the α phase increases with the concentration of the TM alloying elements whereas the Young's modulus and shear modulus are weakened. For the β phase, all the polycrystalline elastic moduli hardens with the addition of the TM alloying elements. The influence of the simple metal (SM) element Al on the elastic properties is much weaker than the TM ones. The TM alloying elements increase the stability of the β relative to the α and ω phases. Al stabilizes significantly the β phase over the ω phase. Our calculations suggest that the d electron density dominates the elastic modulus but not the relative phase stability. The interaction between the TM and SM alloying elements in titanium alloys matters to the relative stability. [ABSTRACT FROM AUTHOR]

Phase decomposition influences significantly the mechanical properties of high entropy alloys (HEAs). Prediction of the phase decomposition of HEA is greatly hindered by the hyper-dimensional composition space of the alloys. In the present work, we propose to represent the HEAs as various pseudo-binary alloys of which the temperature dependent free energies as functions of compositions may be readily calculated by using first-principles methods in combination with thermodynamic models. With the calculated free energies, the phase diagrams of the pseudo-binary alloys may be constructed and the phase decomposition can be predicted. This procedure is applied to Hf-Nb-Ta-Ti-Zr alloy with body-centered cubic (BCC) structure. We predict that the equiatomic HfNbTaTiZr HEA suffers from phase decomposition below critical temperature of 1298 K. The HEA decomposes most favorably to BCC NbTa-rich and HfZr-rich phases. The BCC HfZr-rich phase transfers to a hexagonal close-packed structure (HCP) phase at low temperature. The predicted compositions of the decomposed phases are in good agreement with experiment and Thermal-Calc modeling. Furthermore, the effect of the phase decomposition on the strength of the HEA is evaluated by considering the solid-solution and precipitation strengthening mechanisms. The precipitation strengthening effect is stronger than the solid-solution strengthening at the low annealing temperature but becomes weaker at high annealing temperature. [Display omitted]. [ABSTRACT FROM AUTHOR]