Implementing high entropy alloy synthesis via friction stir processing: Simultaneous solid-state alloying and ultra-refinement of copper

Using the multi-principal element based high entropy alloy (HEA) concept, single-step ultra refinement and solidstate alloying of Cu with NiTi, Y, Fe, Cr, and Co were achieved simultaneously for the first time via friction stir processing (FSP). A bimodal microstructure with an average grain size smaller than 1.5 mu m was attained. The microstructure consisted of inter-dispersed regions of high and low density of geometrically-necessary dislocations. The fraction of high-angle grain boundaries was observed to increase from -33% in the unstirred region to -80% in the processed alloy. Intercalated bands having sharp variations in grain size were formed in conjunction with the bimodal microstructure. The entropic stabilization due to addition of diverse elements assisted multifaceted heterogeneity and grain refinement along. This study paves the way for the development of HEAs via FSP.