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Although high entropy alloys (HEAs) have captured significant attention over the years, the nanocrystalline microstructure of HEAs, similar to that of conventional alloys, is unstable against grain growth. Our initial experimental results have revealed that the hardness of nanocrystalline CoCrFeNi HEA, measured as 517.8 ± 25 HV, decreased substantially to 221.5 ± 11 HV after 1 h of annealing at 1100 °C, and continued to decrease with prolonged annealing, reaching 184 ± 6.4 HV as the annealing time was extended. This study has examined the effect of 1% and 2% Sm solute additions for structural stability and hardness changes of nanocrystalline CoCrFeNi HEAs upon temperature exposures up to 1100 C and for durations up to 24 h. The structural analysis was performed using XRD as a function of annealing time and temperature, and mechanical changes were studied through hardness measurements. It was determined that Sm addition helps the CoCrFeNi HEA retain its high hardness even after 24 h of annealing at 900 °C. This is attributed to the presence of the rare earth element Sm and the formation of Sm-based mixed oxide phases.
Keywords: high entropy alloys, grain growth, annealing, hardness, thermal stability, nanocrystalline© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.