Fabrication and mechanical properties of light weight high strength $Al_{0.3}CoCrFeMnNi$ high entropy alloy

Abstract

Discovery of new alloys has always projected civilization forward. Commonly, alloys are synthesized with one or two main elements with addition of minor elements to further improve material properties. High Entropy Alloys (HEAs) however, provide a new approach to the creation of new alloys, which allows many new combinations of elements which has never been explored. By combining five or more elements with equiatomic distribution, a plethora of new alloys can be created. In general, HEAs are benefited by severe lattice distortion effect and sluggish diffusion effect, which will benefit mechanical properties and thermal stability. Amongst the many combinations of HEA systems possible, CoCrFeMnNi is one of the highly researched systems. It has high hardenability, ductility, and increased mechanical properties at cryogenic temperatures. However, its low yield strength severely limits possible applications of this HEA. To improve mechanical properties, solid solution strengthening and dispersion strengthening was selected. Solid solution strengthening was achieved by addition of aluminum. Further strengthening is also achieved by addition of $Y_2O_3$ . In this study, $Al_{0.3}CoCrFeMnNi$ with different $Y_2O_3$ contents are synthesized by Mechanical Alloying and Spark Plasma Sintering. Addition of aluminum added a BCC phase within the originally sole FCC microstructure and also increased solid solution strengthening. While addition of $Y_2O_3$ increased yield strength greatly due to dispersion strengthening.