The role of entropy in phase stability and mechanics of multi-principal element alloys

In the past two decades, materials science has witnessed a remarkable breakthrough with the introduction of multiple principal elements into a single-phase crystal, leading to a conceptual revolution in physical metallurgy known as multi-principal elemental alloys (MPEAs) or high-entropy alloy (HEAs). These alloys exhibit a unique characteristic where chemical short-range order (SRO) is formed due to the competition between enthalpic and entropy interactions. However, the underlying physical mechanism behind SRO formation remains incompletely understood, and its impact on the mechanical properties of MPEAs is still being explored. In this presentation, I will elucidate the process of chemical disorder-order transition in solid solutions by examining the free energy of the alloy configuration. Through atomistic simulations, I will discuss the role of SRO in phonon instability, diffusion, and dislocation plasticity. Furthermore, I will emphasize the significance of vibrational and configurational entropy in comprehending the thermodynamic stability and deformation mechanisms of MPEAs. These atomistic insights help provide a foundation for the property control is such promising alloys.