Lattice distortion-induced sluggish phase transition in CoCrFeNi_xAl_1-x (x = 0.5, 0.75) high-entropy alloys at high pressures

Abstract

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, CoCrFeNi x Al 1-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 CoCrFeNi 0.5 Al 0.5 and fcc CoCrFeNi 0.75 Al 0.25 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.

Characterization of Nucleation Behavior in Temperature-Induced BCC-to-HCP Phase Transformation for High Entropy Alloy

“…Further, the lattice distortion or deviation from the BCC packing for the 'unknown' type atoms was analyzed. In HEAs, the lattice distortion ε caused by atom size difference has been simplified as [43]:…”

“…Thermal fluctuation or atom vibration has influence on lattice distortion, in addition to atom size differences [43,44]. Therefore, the influence of thermal fluctuation on the nucleation behavior of BCC-to-HCP transformation in HfNbTaTiZr HEA was further studied.…”