Dynamic compressive properties and microstructural evolution of Al1.19Co2CrFeNi1.81 eutectic high entropy alloy at room and cryogenic temperatures

Abstract

The development of aerospace and military defense sectors has put forward higher requirements for the mechanical properties of metals under extreme conditions. Eutectic high entropy alloys (EHEAs) show a wide potential application in these fields due to their superior mechanical performances and good castability. Here, we systematically investigated the dynamic compressive properties and microstructural characteristics of the Al1.19Co2CrFeNi1.81 EHEA at room temperature (298 K) and liquid nitrogen temperature (77 K). The EHEA exhibits an excellent strength-plasticity combination, especially at the strain rate of 4300 s−1 at 77 K, showing a yield strength of 1365 MPa and a true plastic strain over 40%. The underlying deformation mechanisms were uncovered using transmission electron microscopy, revealing that the deformation mechanism is dominated by dislocation slip at 298 K. However, at 77 K, nanotwins together with dislocation slip dominate the plastic deformation. Meanwhile, profuse relatively stable structures are formed due to the interactions between stacking fault (SF)-SF, dislocation-twin boundary and nanotwin-nanotwin, which can effectively inhibit dislocation movement and contribute to a superior strain hardening ability. The adiabatic shear band forms in the late stage of dynamic deformation, and the fractographic observations show a transition from ductile to mixed ductile–brittle fracture mode with decreasing temperature.