Phase transformation pathways and microstructural engineering for high-entropy alloys

Most HEAs are multiphase at equilibrium. Even though some HEAs could be single-phase solid solutions at elevated temperatures, they are extremely weak during high-temperature deformation such as creep. Thus, high-temperature applications require multiphase HEAs. The complicated phase stabilities and diverse diffusional phase transformation pathways in HEAs offer ample opportunities to engineer novel microstructures for desired properties. Yet, navigating this multidimensional space through experimental means can be a formidable challenge. Our approach aims to develop microstructurally engineered multi-phase refractory HEAs (RHEAs) by understanding the relationships among composition, atomic size and elastic modulus mismatches, phase stabilities, transformation pathways, and multi-phase microstructures. Through high-throughput CALPHAD thermodynamic modeling and phase-field simulations, complemented by experimental efforts, we identify the critical alloy and processing parameters affecting the microstructure development and develop microstructure maps to guide experimental efforts. Our results illustrate a rich variety of novel two-phase microstructures could be engineered through various transformation pathways present in RHEAs, which may offer solutions to enhance the mechanical properties of multi-phase RHEAs.