Effects of temperature and strain rate on plastic deformation mechanisms of nanocrystalline high-entropy alloys

The nanocrystalline high-entropy alloys (HEAs) can be regarded as ideal substitution materials for use in aero engines due to their outstanding mechanical properties. Owing to the crucial importance on the evaluation of mechanical properties in nanocrystalline HEAs, the identification of the plastic deformation mechanism remains a challenging topic. Considering the fact that nanocrystalline HEAs suffer from the high-temperature service, the roles of strain rate and temperature on their deformation characteristics should be examined. Here, we report the impact of strain rate and temperature on the mechanical properties and deformation behaviors of nanocrystalline HEAs. This issue was investigated by a series of molecular-dynamics tensile tests at different strain rates ranging from 5 x 10(7) to 1 x 10(10) s(-1) and temperatures ranging from 10 to 1,200 K. The results show that the dislocation slip controls the preferred deformation mechanism at low temperatures and high strain rates. When the temperature rises and strain rate reduces, grain-boundary sliding dominates the primary deformation mechanism at elevated temperatures. Moreover, the occurrence of the face-centered-cubic (fcc) to body-centered-cubic (bcc) phase transformation can effectively enhance the plasticity of HEAs. The synergistically-integrated experimental and modeling efforts at the nanoscale will help understand, control, and optimize the mechanical behaviors of nanocrystalline HEA systems, thereby enabling the development of advanced nanocrystalline HEAs.