In situ atomic-scale observation of deformation-induced reversible martensitic transformation in a CrMnFeCoNi high entropy alloy

High entropy alloys (HEAs) have attracted much attention for their excellent mechanical properties stemming from diverse deformation mechanisms. Particularly, face-centered cubic (FCC) to body-centered cubic (BCC) martensitic transformation is crucial for enhancing the strength and plasticity of HEAs, particularly at cryogenic temperatures. However, the fundamental atomic mechanism underlying martensitic transformation remains elusive, and the impact of martensitic transformation on the mechanical properties of HEAs at room temperature is unknown. Here, we report in situ atomic-scale observation of a reversible martensitic transformation from FCC to body-centered tetragonal (BCT) and ultimately back to FCC in the nanostructured CrMnFeCoNi HEA at room temperature under deformation. This martensitic transformation is completed by the synergistic action of 90 degrees partial dislocations slip on (111)FCC plane and atom shuffling, involving the periodic arrangement and slip of two 90 degrees half Shockley partial dislocations a /12[1 1 2] (111) and one 90 degrees Shockley partial dislocation -a /6[1 1 2] (111) on three successive (111)FCC atomic planes. Additionally, the reversible phase transformation induced by high stress dissipates strain energies and hinders crack propagation, thereby enhancing the fracture toughness of HEAs. Our findings contribute to a deeper comprehension of the martensitic transformation mechanisms in HEAs, offering valuable insights for improving their mechanical properties. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.