Formation, reverse transformation, and properties of ε-martensite phase in the CoCrFeMnNi high-entropy alloy under high-pressure

A CoCrFeMnNi high-entropy alloy (HEA) was compressed at 20 GPa and room temperature, 500 °C, and 800 °C, respectively. We examined the microstructure and reverse transformation of the hexagonal close-packed (hcp) phase and its influence on the properties of the HEA after compression. The hcp laths with a width of several nanometer formed after compressed at room temperature, and kept the Kurdjumov-Sachs oriental relationship with the face-center-cubic (fcc) phase. During annealing, partial hcp laths transformed reversely into the fcc-structured nano twins. The influence of the hcp phase on the hardness of the HEA was discussed. In addition, the in situ resistance measurement also proved the fcc-to-hcp transition.