Toward excellent tensile properties of nitrogen-doped CoCrFeMnNi high-entropy alloy at room and cryogenic temperatures

Here, the effect of nitrogen addition on the microstructural evolution and mechanical properties of the alloys at 298 K and 77 K was investigated. In the CoCrFeMnNi alloys with and without nitrogen, the two types of precipitate (Cr2N and σ, respectively) were formed. These precipitates suppress the grain growth of the alloys through the Zener pinning effect during heat treatment, which contributes to strengthening induced by grain boundary and precipitate. In particular, the Cr2N precipitate affects the grain refinement and precipitation strengthening more efficiently compared to the σ phase. The planar configuration of dislocations was observed in the deformed alloys at 298 K, and the deformed microstructure developed into stacking faults and deformation-induced twinning at 77 K. Accordingly, the nitrogen-doped CoCrFeMnNi alloy exhibits excellent ultimate tensile strength and elongation with substantial strain hardening. The strong temperature dependence of yield strength of the nitrogen-doped and nitrogen-free alloys was presumably conjectured that it is associated with the large friction stress induced by strongly temperature dependent short-range thermal obstacles.