Grain size effects on mechanical behavior of Al_0.25CoCrFeNi high-entropy alloy at room and cryogenic temperatures

FCC high-entropy alloys (HEAs) exhibit excellent strain hardening capabilities at both room and cryogenic conditions due to deformation mechanisms such as twinning and stacking faults. Recent studies have focused on further enhancing the strength of FCC (face-centered cubic) HEAs through grain refinement. However, the impact of grain size on the mechanical properties and deformation behavior of these alloys still requires further investigation. This study examines the microstructure and mechanical behavior of Al_0.25CoCrFeNi HEA with three distinct grain sizes. As the grain size decreases, the yield strength at both 25 °C and −196 °C increases due to grain boundary strengthening. Notably, the Hall-Petch coefficient at −196 °C is slightly higher than that at 25 °C. At 25 °C, the deformation mechanism transitions from dislocation slip to deformation twinning as the grain size increases. At −196 °C, deformation twins are observed in fine-grained samples, with their density increasing and spacing decreasing as the grain size increases. The refinement of nanotwins promotes a dynamic Hall-Petch effect and enhances the strength-ductility balance, attributing to the increase in flow stress and the reduction in stacking fault energy at −196 °C. This study provides valuable insights into the effect of grain size on the deformation mechanisms of alloys at room and cryogenic temperatures.