Negative enthalpy-induced phase decomposition and transformation in Fe-35Ni-10Al medium entropy alloy

The complex mixing enthalpy, arising from multiple atomic interactions among constituent elements, significantly influences the phase stability of high-entropy alloys, in conjunction with high configurational entropy. In this study, we investigate the phase decomposition and transformation behaviors of the Fe-35Ni-10Al (at.%) medium-entropy alloy through a combination of multiscale characterization techniques and thermodynamic analysis. The aging temperature plays a pivotal role in phase decomposition, transitioning from the FCC phase to the L1₂-Ni₃Al and B2-NiAl phases, driven by the interplay of thermodynamic and kinetic factors. We analyze the enthalpy of formation, elemental diffusion, and interfacial energy required for nucleation to explain the formation of the L1₂-Ni₃Al phase and its subsequent transformation into the B2-NiAl phase. This work provides deeper insights into the phase decomposition and transformation pathways in medium-entropy alloys, crucial for tailoring their unique microstructures and mechanical properties, which will aid in the further development of high-entropy alloys.