CALPHAD predictions and microstructural evolution of high-entropy alloy fabricated by spark plasma sintering

This study investigates the thermodynamic predictions and microstructural evolution of Co₁₀Cr₂₀Cu₂₀Mn₂₀Nb₁₀Ni₂₀ High-Entropy Alloy (HEA) fabricated via Spark Plasma Sintering (SPS). Using the CALPHAD method through Thermo-Calc software and employing the TCHEA2 database, equilibrium phase compositions were predicted across a temperature range of 850–950 °C. The HEA powder was mechanically alloyed and sintered at three temperatures to assess densification, phase stability, and microstructural transformations. CALPHAD simulations predicted a multiphase system dominated by FCC_L12, accompanied by BCC_B2 and C14_Laves intermetallic phases. XRD, SEM, and EDS analyses confirmed these phases in the sintered samples, thus highlighting a thermodynamic alignment between simulation and experiment. Increased sintering temperature led to enhanced densification (with relative density of 98.8 % at 850 °C, 99.1 % at 900 °C and 99.3 % at 950 °C), phase homogenization, and microhardness, with values rising from ∼343 HV at 850 °C to ∼443 HV at 950 °C. The study further clarifies how equilibrium CALPHAD predictions translate under SPS conditions and suggests an optimal SPS window for the studied Cu–Nb-rich HEA. It also shows the synergy between computational modelling and advanced manufacturing in tailoring HEA microstructures and properties.