Synthesis of Multi-Principal Element Alloys by a Conventional Powder Metallurgy Process

The development of tailored microstructures of Multi-principal element alloys (MPEAs) is currently a hot topic in physical metallurgy. The most targeted systems are equimolar alloys composed of 3d transition metals including the so-called Cantor alloy (i.e. CoCrFeMnNi) and derivatives such as CoCrFeNi and CoCrFeNiAlx. Powder metallurgy is a promising route for this purpose and include manufacturing techniques such as hot pressing of mechanically activated or prealloyed powders or the less popular press-sinter route of mixed powders. In this work, cold pressing followed by fast vacuum sintering (1h) at various temperatures (Tmax =1100-1300 °C) of mixed powders of CoCrFeNi and CoCrFeNiAl0.4 were explored for the synthesis of structurally and chemically homogeneous alloys. This approach is promising for the synthesis of bulk alloys of higher purity with respect to hot pressing of mechanically prealloyed powders. Microstructural investigations were performed by X-ray Powder diffraction (XRPD) and Scanning electron microscopy (SEM). It will be shown that the reactive sintering kinetics of the investigated systems require a Tmax of 1200 °C for effective alloying at the short holding time employed for CoCrFeNi. Instead, 1300 °C is needed for CoCrFeNiAl0.4.