Temperature-Dependent Mechanical Properties of Ni-Based Concentrated Alloys: Insights from First-Principles Calculations

The present work focuses on predicting temperature-dependent mechanical properties of Ni-based concentrated alloys Ni₁₈Cr₁₀Co₁₀Fe₆M₄ (abbreviated by X₄₄M₄, with M = Al, V, Mn, Fe, Nb, Mo, and W) using density functional theory (DFT). These predictions are based on shear (plastic) and elastic deformations, utilizing the special quasirandom structure (SQS), the phonon-based quasiharmonic approach (QHA), and the quasistatic approach. The resulting properties include coefficient of thermal expansion via QHA, ideal shear strength (τ_IS), and stable and unstable stacking fault energies (γ_SF and γ_US) through pure alias shear deformation, and elastic constants (c_ij), bulk modulus (B₀), and shear modules (G₀) via elastic deformation. Notably, predicting accurate γ_SF is challenging due to uncertainties that can exceed the γ_SF values. τ_IS and γ_US exhibit a strong linear relationship, enabling the accurate prediction of γ_US based on the precisely determined τ_IS. All mechanical properties of X₄₄M₄ decrease with increasing temperature, except for some γ_SF cases such as X₄₄M₄ with M = V, Mn, Fe, Mo, and W. Among the X₄₄M₄ alloys, X₄₄Nb₄ exhibits the lowest τ_IS, γ_US, and G₀ values, and the highest B₀/G₀ ratio, while X₄₄Mn₄ has the lowest B₀ and B₀/G₀ ratio. We found that volume is a crucial descriptor for understanding and modeling mechanical properties (except B₀ and maybe also γ_SF) affected by alloying elements and temperature. Ni-based dilute alloys (e.g., Ni₁₁M₁ and Ni₃₁M₁) and concentrated alloys (e.g., X₄₄M₄) show similar trends in mechanical properties influenced by alloying elements and temperature, simplifying the analysis and design of Ni-based alloys.