High Entropy Materials Enabled by Microwave-Induced Plasma

High Entropy Alloys (HEAs) and ceramics typically consist of five or more principal components that form a solid solution structure, instead of complex phases (e.g., intermetallics), and are stabilized by their high configurational entropy of mixing. We recently demonstrated a unique approach to synthesis of high entropy materials, including HEAs, enabled by microwave (MW)-induced plasma. This approach goes beyond conventional slow radiative heating by combining rapid MW energy absorption with enhanced chemical kinetics afforded by a plasma discharge. Conventional HEA formation relies on melting or long durations of intense mechanical agitation/alloying, often followed by subsequent heating/sintering steps to finally convert the mixture into a HEA solid solution. Our approach, facilitated by density functional theory calculations of entropy forming ability descriptors, involves thermal reduction of a five-component transition metal oxide powder mixture in a plasma reducing environment performed efficiently as a single step. Hardness and oxidation resistance measurements of the plasma-synthesized high entropy materials reveal substantial improvement over their non-HE counterparts. Current work is aimed at investigating reaction kinetics/pathways for HE materials made using this approach. Through the unique combination of plasma reduction of metal oxide precursors with the benefits of rapid MW heating/cooling, we anticipate highly efficient synthesis and fine microstructural control of HE alloy and ceramic systems.