Heat treatments' effects on the microstructure and mechanical properties of an equiatomic Al-Cr-Fe-Mn-Ni high entropy alloy

The microstructure and properties of an equiatomic AlCrFeMnNi high entropy alloys (HEA) in the as-cast and heat treated conditions are presented. Using a variety of advanced characterization methods, it is shown that the AlCrFeMnNi solidified dendritically with Cr, Fe and Mn rich dendrite cores (DC) and Al and Ni rich interdendritic (ID) regions. Upon cooling, during solidification, AlCrFeMnNi alloy underwent spinodal decomposition. The DC area decomposed to a mixture of B2 and FCC matrix with nano cuboid BCC precipitates, while the ID region decomposed to a BCC matrix with B2 precipitates. The combination of relatively soft DC surrounded by hard ID regions resulted in high compressive strength combined with large compressive ductility and can be regarded as a “macro” composite material. The cracks initiate and propagate in the harder and more brittle ID regions. Heat treatments increased the amount of the FCC phase and enhanced microstructural coarsening. The undesirable σ phase was not detected after any heat treatment.