Using Density Functional Theory (DFT) calculations and Monte-Carlo (MC) simulations, we investigate the recently reported magnetic transition in B2 Al–Cr–Co alloys. The Cr sublattice is alloyed with different amounts of Co in the antiferromagnetic (AFM) B2 AlCr binary alloy and the resulting exchange interactions are analyzed within the Heisenberg Hamiltonian framework. DFT results reveal that at low Co concentrations the system favors the AFM order, while at high Co contents a transition to the ferromagnetic (FM) state is observed. Within the FM stability field, the Curie temperature (T_C), obtained within the mean-field approximation, is below ∼160 K and decreases with Co concentration. The calculated exchange parameters evolve systematically with Co content, and the trends are consistent with the DFT total energies. The magnetic configurations obtained from MC simulations follow the DFT results at low Cr levels but predict a spin-glass behavior for alloys containing more than 40 at. % Co on Cr sublattice. These findings provide a fundamental understanding of how the chemistry-driven changes in exchange interactions affect magnetism in the B2 Al–Cr–Co alloys.

The underlying mechanism of co-segregation of alloying elements at the grain boundary and its influence on mechanical properties are elaborated in Mg-Zn-Ca alloys by integrated experimental characterizations and ab initio calculations. Significant co-segregation of Zn and Ca at the grain boundary is detected in the Mg-Zn-Ca ternary alloy, leading to an important contribution to the simultaneous improvement of strength and ductility. The relatively strong electronic interactions between Zn and Ca are demonstrated to promote the formation of Zn-Ca ionic bonds and greatly decrease the segregation energy. It, in combination with the atomic-size-related preferred occupations of Zn and Ca, primarily contributes to their significant co-segregation at the grain boundary. The obvious co-segregation of Zn and Ca remarkably decreases grain size, significantly contributing to the improved strength. In addition, coarse twins and the associated cracking are efficiently suppressed in plastic deformation owing to the decreased grain size. Furthermore, the co-segregation significantly increases grain boundary cohesion strength and decreases grain boundary energy, which can delay the initiation of grain boundary cracks and accommodate high stress to activate non-basal slips. In addition, the high-angle grain boundaries stabilized by alloying element co-segregation promote the transmission of non-basal slip pairs and stress relaxation at the grain boundary and improve ductility ultimately. The present advances enhance the understanding required for evading the strength and ductility trade-off in Mg alloys by tailoring alloying element segregation.

In this study, novel non-equiatomic CoCrFeMnNi-based medium- and high-entropy alloys (M/HEAs) were designed to activate distinct deformation mechanisms, including twinning-induced plasticity (TWIP) and/or transformation-induced plasticity (TRIP). Tensile tests were performed at 298 and 173 K. A variety of ex-situ multiscale characterization techniques, strengthening modeling, thermodynamic modeling (CALPHAD method), and ab initio density functional theory (DFT) calculations were employed to investigate the structural and microstructural evolution, enabling accurate identification of the strengthening and active deformation mechanisms operating in the M/HEAs. Strengthening modeling revealed that grain boundary strengthening was the primary contributor to yield strength at both temperatures. A key finding of this study is that a controlled FCC→HCP martensitic transformation, associated with TRIP, enhances the strength-ductility balance even when the resulting HCP phase reaches ∼50% volume fraction. This demonstrates that TRIP-enabled metastability engineering is a promising strategy for designing high-performance M/HEAs for next-generation structural applications in energy, aerospace, and defense.

The nonstoichiometric Fe2⁢P-type FeMn(1−𝑥)⁢V𝑥⁢(P0.5⁢Si0.5)1−𝑥 alloys (𝑥=0,0.01, 0.02, and 0.03) have been investigated as potential candidates for magnetic refrigeration near room temperature. The magnetic ordering temperature decreases with increasing FeV concentration 𝑥, which can be ascribed to decreased ferromagnetic coupling strength between the magnetic atoms. The strong magnetoelastic coupling in these alloys results in large values of the isothermal entropy change (Δ⁢𝑆𝑀); 15.7 J/(kg K), at 2 T magnetic field for the 𝑥=0 alloy. Δ⁢𝑆𝑀 decreases with increasing 𝑥. Results from Mössbauer spectroscopy reveal that the average hyperfine field (in the ferromagnetic state) and average center shift (in the paramagnetic state) have the same decreasing trend as Δ⁢𝑆𝑀. The thermal hysteresis (Δ⁢𝑇hyst) of the magnetic phase transition decreases with increasing 𝑥, while the mechanical stability of the alloys improves due to the reduced lattice volume change across the magnetoelastic phase transition. The adiabatic temperature change Δ⁢𝑇ad, which highly depends on Δ⁢𝑇hyst, is 1.7 K at 1.9 T applied field for the 𝑥=0.02 alloy.

The structural, elastic and electronic properties of the ternary transition metal nitrides alloys TaxHf1−xN at (0<x<1) in the rock-salt structure are investigated by ab initio calculations. The calculations were performed using the first-principles Exact Muffin-Tin Orbitals method using full charge density technique within the framework of density functional theory. The compositional disorder is treated within the coherent potential approximation. The estimated formation enthalpy indicates that Ta0.5Hf0.5N is thermodynamically the most stable alloy. The obtained lattice parameters of the TaxHf1−xN alloys are in good agreement with other available theoretical and experimental values. The predicted elastic stiffness constants C11, C12 and C44 indicate that the TaxHf1−xN alloys are mechanically stable and the addition of Ta increases their ductility. The Ta0.7Hf0.3N found to be hardest alloy. The correlation between Pettifor's criterion (C12−C44) normalized by bulk modulus B and Pugh's ratio G/B with increasing the degree of alloying x allowed us to predict that the critical value (G/B)=0.53, which correspond to x around 0.6±0.05, marks the brittle to ductile transition.

First, we discuss a common feature of single-phase pure metals and amorphous and high-entropy alloys: the maximum value of hardness corresponding to a valence electron count (VEC) value of around 6.5-7. This correlation is explained by the coincidence that by subtracting the number of sp valence electrons (Nsp = 2) from the VEC we obtain the maximal number of unpaired d electrons, Nd = 4.5-5 in the 3d, 4d, and 5d rows of transition elements. These unpaired d electrons form orbital overlap bonding, which is stronger than the isotropic metallic bonds of a delocalized electron cloud. The more unpaired d electrons there are, the higher the bonding strength. Second, we will discuss the hardness formulas derived from cohesion energy and shear modulus. We will demonstrate that both types of formulas originate in the electrostatic energy density of metallic bonds, expressing a 1/R4 dependence. Finally, we show that only two parameters are sufficient to estimate hardness: the atomic radius and the cohesion-based valence. In the case of alloys, our formula gives a lower bound on the hardness only. It is not suitable for calculation of the hardness increase caused by solid solution, grain size, precipitation, and phase mixture.

Gold (Au) segregation at Pt grain boundaries (GBs) plays an important role in the properties of Pt-based alloys. It was reported that close-packed GBs and open GBs exhibit different segregation behaviors, and their origin is still unclear. Based on the density functional theory as implemented in the exact muffin-tin orbitals method and the full charge density technique, we investigate the impact of bulk composition and temperature on the segregation behaviors of the Σ 3 ( 111 ) [ 1 1 ¯ 0 ] , Σ5(310)[001], and Σ 9 ( 221 ) [ 1 1 ¯ 0 ] symmetric tilt GBs in Pt-Au alloys. It is revealed that the segregation driving forces are correlated with the large local volume near the GB and the miscibility gap in Pt-Au alloys. At finite temperatures when the configurational entropy is considered, a competition between the chemical driving force and the configurational entropy is responsible for the segregation anisotropy in Pt-Au alloys. The bulk composition has a small effect on the segregation energy but strongly impacts the equilibrium concentration profiles at finite temperatures. The present study provides a theoretical analysis for the segregation anisotropy, and the methodology utilized in this work can be generalized to other binary or multi-component dilute or concentrated alloys while the composition variation is involved.

The formation energy of the coherent interface between the primary strengthening phase γ ′ ′ and γ matrix in Inconel 718 alloy is investigated using ab initio calculations. We begin by examining the interface energy of the ordered Ni/Ni 3 Nb system. A negligible interface energy (1 mJ/m 2 ) is obtained for the nonmagnetic state, which is explained by a nearest-neighbor layer interaction model. Allowing for spin polarization within both face-centered cubic (FCC) and D0<inf>22</inf> structures increases the interface energy to 181 mJ/m 2 . The strong magnetic dependence of the formation energy of the ordered Ni/Ni 3 Nb interface arises primarily from the different magnetic behavior of Ni in FCC and D0<inf>22</inf> phases. A detailed analysis of the site preference of minor elements in the γ ′ ′ phase shows that Fe and Cr occupy the Ni-site, while Al, Mo, and Ti tend to occupy the Nb-site. The coherent interface energy of the γ / γ ′ ′ interface is predicted to be 257 mJ/m 2 for the paramagnetic state and 255 mJ/m 2 for the ferromagnetic state. The closeness of these formation energies reflects a similar magnetic response from both phases. The sensitivity of the γ / γ ′ ′ interface energy to variations in the γ and γ ′ ′ compositions is also investigated. Only small variations are revealed for the reported composition intervals. Our predictions serve as input for further theoretical simulations and as a reference for experimental investigations.

This study employs ab initio density functional theory (DFT) combined with the exact muffin-tin orbitals (EMTO) method and coherent potential approximation (CPA) to systematically investigate the structural and mechanical properties of TiVNbMo-based refractory high-entropy alloys (RHEAs) doped with 4d transition metals (Zr, Rh, Ag). Equiatomic TiVNbMoM (M = Zr, Rh, Ag) and non-equiatomic Ti(1−x)VNbMoMx, TiV(1−x)NbMoMx, TiVNb(1−x)MoMx and TiVNbMo(1−x)Mx (with M = Zr, Rh, Ag; 0 ≤ x ≤ 1), were analyzed to evaluate phase stability, lattice parameters, elastic constants, and mechanical moduli. Results confirm the dominance of the body-centered cubic (bcc) phase in all equiatomic alloys, with valence electron concentration (VEC = 4.8-6.2) and atomic size difference (δ = 3.65%-6.18%) aligning with solid-solution formation criteria. However, Zr doping reduces bcc stability by lowering average d-electron occupancy, while Rh and Ag retain bcc dominance. Zirconium significantly expands the lattice parameter, whereas Rh reduces it. Mechanical analysis reveals that Rh enhances hardness in Rh-rich compositions, while Zr substitution at Ti sites improves ductility. All systems exhibit ductility (B/G > 1.75; ν > 0.31). This study provides the first theoretical exploration of Rh and Ag doping effects on TiVNbMo RHEAs, demonstrating Rh’s unparalleled hardening capability and Zr’s dual role in lattice expansion and ductility enhancement. These findings, validated against experimental lattice constants and hardness, as well as theoretical elastic constants and moduli, require further experimental studies to confirm and extend the theoretical predictions.

Using first principle alloy theory, we calculate the basal stacking fault energies as a function of chemical composition for a series of Mg binary alloys by accounting for the chemical disorder in solid solution. We show that while the basal stacking fault energies significantly increase with the addition of Co, Ni, Ag, and Li, they obviously decline upon alloying with Sn, Y, Ca, and Al. In contrast, Zn and Ti exhibit negligible influence on the basal stacking fault energy of I1 and I2 fault. The varied influence of alloying species on basal stacking fault energies are demonstrated to predominately determined by the volume- and composition-dependent relative phase stability between face-centered cubic and hexagonal close-packed structure. The influence of alloy species predicted in solid solution are obviously different from those computed for segregated ones, underlining the significance of chemical disorder to the intrinsic energy barriers of Mg solid solutions.