Interdiffusion‐Driven Phase Growth in Cr ₂₆ Co ₂₀ Fe ₂₀ Mn ₂₀ Ni ₁₄ /Al High‐Entropy Alloy Diffusion Couple

This study examined the nucleation and kinetics of phases progressed during the interdiffusion couple annealing of an extremely low stacking fault energy (SFE) Cr 26 Co 20 Fe 20 Mn 20 Ni 14 high‐entropy alloy (HEA) interfaced with pure Al at 600°C, up to 240 h. Microstructural analysis revealed two primary phases (indicated as P1 and P3) at all annealing intervals and region P2, which was a mixture of P1 and P3. The characterizations confirmed the phases P1 and P3 to be Al 9 (Co, Cr, Ni, Mn, Fe) 2 and Al 5 (Co, Cr, Ni, Mn, Fe) 2 , respectively. A transition zone with segregated phases P4 (Co, Ni‐rich) and P5 (Cr, Fe, Mn‐rich) was observed close to the HEA interface. Thermodynamic phase formation tendencies were further validated through CALPHAD (Calculation of Phase Diagram)‐analyses. Phase growth across the interdiffusion zone attains parabolic law with a rate constant ( K p ) of 1.35 × 10 −14 m 2 /s. The results indicated that the formation of intermetallic phases was primarily driven by enthalpy considerations. However, the existence of multiple elements in the sublattices delineated that entropy stabilization also played a significant role in the phase formation.