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The present work investigates how the vanadium (V) content in a series of Al50V x (Cr0.33Mn0.33Co0.33)(50−x) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (T C) of the BCC phase in comparison with the B2 phase. We find that lower V content increases the B2 phase fraction, the saturation magnetization, and the Curie point, in line with the calculations. This trend is primarily connected with the preferential partition of V in the BCC phase, which however hinders the theoretically predicted antiferromagnetic B2 phase stabilizing effect of V. On the other hand, the chemistry-dependent properties of the ferromagnetic B2 phase suggest that a careful tuning of the composition and phase fractions can open the way towards promising high-entropy magnetic materials.

Recent advances in tuning the long-standing strength-ductility tradeoff have drawn attention to high-entropy alloys (HEAs), and the appearance of hexagonal close-packed (hcp) structures has been emphasized. However, few studies have explored the elastic moduli of hcp HEAs, which is of prime importance for improved understanding of the outstanding mechanical properties. In this work, we focus on a set of equiatomic rare-earth-free HEAs with hcp structures, i.e. ScTiZr, ScTiHf, ScZrHf, TiZrHf, and ScTiZrHf, and their thermo-elastic properties are studied using quantum mechanical first-principles methods. It is found that, for all considered HEAs, the hexagonal axial ratio shows a weak dependence on the temperature effect, and the thermal expansion coefficient remains almost unchanged above room temperature. From the calculated temperature-dependent single-crystal elastic constants, we analyzed the mechanical stability, elastic anisotropy, and derived polycrystalline moduli. Results indicate that the present HEAs exhibit rather high elastic isotropy and large elastic softening resistance. The ab initio predicted Young’s modulus, shear modulus, and specific modulus do not obey the rule of mixture, which indicates that there exists a strong intrinsic hardening effect in all of the considered HEAs. The calculated results are in good agreement with the available experimental measurements.

First-principles total-energy calculations were performed for the trigonal shear elastic constant (C44) of body-centred cubic (bcc) V and Nb. A mechanical instability in C44 is found for V at pressures of ~2 Mbar which also shows a softening in Nb at pressures of ~0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0

Special quasi-random structure (SQS) and coherent potential approximation (CPA) are techniques widely employed in the first-principles calculations of random alloys. Here we scrutinize these approaches by focusing on the local lattice distortion (LLD) and the crystal symmetry effects. We compare the elastic parameters obtained from SQS and CPA calculations, taking the random face-centered cubic (fcc) Ti1-xAlx (0

The Al(x)MoNbTiV (x = 0-1.5) high-entropy alloys (HEAs) adopt a single solid-solution phase, having the body centered cubic (bcc) crystal structure. Here we employ the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to investigate the equilibrium volume, elastic constants, and polycrystalline elastic moduli of Al(x)MoNbTiV HEAs. A comparison between the ab initio and experimental equilibrium volumes demonstrates the validity and accuracy of the present approach. Our results indicate that Al addition decreases the thermodynamic stability of the bcc structure with respect to face-centered cubic and hexagonal close packed lattices. For the elastically isotropic Al(0.4)MoNbTiV HEAs, the valence electron concentration (VEC) is about 4.82, which is slightly different from VEC ∼ 4.72 obtained for the isotropic Gum metals and refractory--HEAs.

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

GaAs1 - xBix alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to ...

Ab initio calculations, based on the exact muffin-tin orbitals method are used to determine the elastic properties of Cu-Au alloys with Au/Cu ratio 1/3. The compositional disorder is treated within the coherent potential approximation. The lattice parameters and single-crystal elastic constants are calculated for different partially ordered structures ranging from the fully ordered L1(2) to the random face centered cubic lattice. It is shown that the theoretical elastic constants follow a clear trend with the degree of chemical order: namely, C(11) and C(12) decrease, whereas C(44) remains nearly constant with increasing disorder. The present results are in line with the experimental findings that the impact of the chemical ordering on the fundamental elastic parameters is close to the resolution of the available experimental and theoretical tools.

We have studied the influence of additions of Al and Si on the lattice stability of face-centred-cubic (fcc) versus hexagonal-closed-packed (hcp) Fe-Mn random alloys, considering the influence of magnetism below and above the fcc Néel temperature. Employing two different ab initio approaches with respect to basis sets and treatment of magnetic and chemical disorder, we are able to quantify the predictive power of the ab initio methods. We find that the addition of Al strongly stabilizes the fcc lattice independent of the regarded magnetic states. For Si a much stronger dependence on magnetism is observed. Compared to Al, almost no volume change is observed as Si is added to Fe-Mn, indicating that the electronic contributions are responsible for stabilization/destabilization of the fcc phase.

The polycrystalline elastic parameters of ferromagnetic Fe(1-x)M(x) (M = Al, Si, V, Cr, Mn, Co, Ni, Rh; 0 ≤ x ≤ 0.1) random alloys in the body centered cubic (bcc) crystallographic phase have been calculated using first-principles alloy theory in combination with statistical averaging methods. With a few exceptions, the agreement between the calculated and the available experimental data for the polycrystalline aggregates is satisfactory. All additions considered here decrease the bulk modulus (B) and Poisson's ratio (ν) of bcc Fe. The complex composition dependence of the C(44) single-crystal elastic constant is reflected in the polycrystalline shear modulus (G), Young's modulus (E), and Debye temperature (Θ). The polycrystalline anisotropy of bcc Fe is increased by all additions, and Al, Si, Ni, and Rh yield the largest alloying effects.

The stacking fault energies are used to illustrate the footprint of magnetism on the mechanical properties of Fe-Cr-Ni alloys forming the basis of austenitic stainless steels. We find that the usua ...