High entropy alloys obtained by field assisted powder metallurgy route: SPS and microwave heating

The aim of this work was to investigate the field assisted powder metallurgy route for producing HEAs at equimolar composition, i.e. FeCoNiCrAl, starting from metal powders. Both mixed, mechanically activated and mechanically alloyed powders have been used. The powders obtained by mechanical alloying were synthesized only by SPS, whereas the remaining ones were sintered by SPS or microwave heating. The investigated field assisted sintering techniques allowed an extremely short alloying time, high energy density on the load and negligible contamination by the surrounding environment. Both the conducted sintering-synthesis technology resulted not definitive to produce chemical homogeneity and to obtain a single stable structure. Thus a subsequently heat treatment was required. The post heat treatment, indeed, led to a single crystalline structure (FCC) and the material was fully recrystallized. After heat treatment samples are isomorphic: they exhibit two different phases with the same FCC cell, but different chemical composition, in detail Fe-Cr richer and Al-Ni richer. SPS-ed samples present a reduced porosity, while microwave processed ones are much more porous and this is reflected in the mechanical properties.