Investigation into synergistic enhancement of strength and reduction in density for novel bimodal-sized Al2O3p reinforced CoCrFeMnNi composites

An in-depth understanding of the bimodal scale particle reinforced composites, including the particle content and size, phase constitution and distribution, and their effects on mechanical properties and deformation mechanisms, is essential to advance the study of high performance high entropy alloys (HEAs). In this study, the bimodal-sized (nano + micron)(N + M)-Al2O3P/CoCrFeMnNi reinforced composites and monomadal-sized micron(M)-Al2O3P/CoCrFeMnNi reinforced composites were successfully fabricated using a two-step ball milling process in conjunction with spark plasma sintering (SPS) technology. Results showed that the Al2O3P/CoCrFeMnNi composites primarily consisted of fcc structure, with Al2O3 and MnAl2O4 as secondary phases. The M-Al2O3P reinforced composites contained obvious heterogeneous structure while (N + M)-Al2O3P reinforced composites exhibited a multi-scale grain structure comprising of double-sized reinforcement and multiple-sized matrix grains. The yield strength (YS) of bimodal-size particle reinforced composites was higher than that of monomadal particle reinforced composites. For example, the YS of (N-5)/(M − 5) and (N-5)/(M − 10) composites was 117% and 133% higher than that of HEA, respectively. Intriguingly, (N + M)-Al2O3P reinforced composites effectively addressed the issue of reduced material strength caused by a high concentration of particles with a monomadal size. Moreover, the composites of (N-5)/(M − 5) and (N-5)/(M − 10) with a high content of lightweight Al2O3P effectively contributed to the reduction in density of HEA, exhibiting a decrease by 11% and 17% compared to pure HEA, respectively.