Lattice distortion-induced sluggish phase transition in CoCrFeNixAl1-x (x =0.5, 0.75) high-entropy alloys at high pressures

High-entropy alloys (HEAs) attract growing interest due to their remarkable properties. However, our knowledge of the mechanism of phase stability of HEAs is still very limited. Herein, CoCrFeNixAl1-x (x = 0.5 and 0.75) were compressed to high pressures to investigate the lattice distortion effect on their phase stability. It was discovered that both bcc CoCrFeNi0.5Al0.5 and fcc CoCrFeNi0.75Al0.25 alloys transform to the hcp structure at high pressures, following a gradual phase transition. The sluggish character of these transitions perhaps originates from the local energy fluctuations caused by the chemical disorder. The phase transitions in both studied compounds commenced when their intrinsic lattice strain had reached the maximum value, indicating that the lattice distortion effect plays a key role in these crystallographic structure-transforming processes. These results provide fundamental information on the phase selection rules of HEAs, which are important for physical metallurgy theories and HEAs design in the future.