Achieving excellent strength-ductility synergy in (Co, Cr)58Ni30Mo6Al6 high entropy alloys by suppressing intermetallic compounds and introducing nanoprecipitates

Precipitation hardening serves as a viable mechanism to enhance the strength of high/medium entropy alloys (H/MEAs). The nature of precipitates in HEAs varies based on the composition of multiple principal elements. In order to further enhance the performance of HEAs across different applications, it becomes imperative to exercise control over phase synthesis and suppress the precipitation of detrimental phases. In this investigation, we propose a strategy for regulating the precipitation of the second phase in (Co, Cr)58Ni30Mo6Al6 (Co/Cr ratio = 1, 1.5, 2, 3) HEAs. Through precise adjustment of atomic ratios, the detrimental σ and μ phases are effectively restrained, while coherent nanoprecipitates are achieved through subsequent aging treatment. These fine nanoscale coherent phases alter the mode of dislocation slip, transforming planar slip into cross-slip, thereby providing a novel mechanism for the strengthening of the alloy. This controlled elimination and precipitation of phase contributes to a hierarchical improvement in the mechanical tensile properties. The aged HEA exhibits exceptional characteristics, including a strength of 1.3 GPa and 31% plasticity at 298 K (1.67 GPa and 40% at 77 K).