Investigating the role of nickel in CoCrFeMnNix high-entropy alloys: thermodynamic analysis and molecular dynamics simulations

Abstract

The influence of Ni content on phase stability and deformation mechanisms in CoCrFeMnNix high-entropy alloys (HEAs) was investigated using high-entropy alloys predicting software descriptors, CALPHAD, and molecular dynamics (MD) simulations. Increasing Ni content raises the valence electron concentration from 7.50 to 8.00, decreases atomic-size mismatch from 3.51% to 3.27%, and shifts the mixing enthalpy and Gibbs free energy toward more negative values, indicating improved solid-solution stability. CALPHAD calculations show that Ni enhances face-centered cubic (FCC) stability while reducing the equilibrium tendency of secondary phase formation. MD relaxation reveals progressive lattice contraction and increasingly negative cohesive energies, suggesting enhanced energetic stability of the FCC-based random solid-solution models. Under constrained uniaxial-strain tensile deformation at 300 K, all compositions exhibit comparable axial stiffness (∼176–183 GPa) and ultra-high peak axial stresses (∼18–20 GPa) characteristic of defect-free single-crystals. Among the investigated alloys, equiatomic CoCrFeMnNi shows the highest ideal tensile resistance. Plastic deformation is governed primarily by Shockley partial dislocation activity, stacking-fault formation, and HCP-like faulted regions. Generalized stacking fault energy (SFE) calculations show that Ni addition increases the unstable stacking fault barrier from approximately 167.84–224.09 mJ m−2, while shifting the intrinsic SFE from −63.59 to −30.59 mJ m−2. The negative intrinsic stacking fault energies indicate that HCP-like faulted configurations are energetically favored relative to the FCC reference at 0 K within the employed 2NN-MEAM framework. However, the progressive shift toward less negative values with increasing Ni content shows that Ni makes these faulted configurations progressively less favorable while increasing the resistance to leading Shockley partial nucleation.