Deformation mechanisms of Al_0.1CoCrFeNi at elevated temperatures

Deformation mechanisms of a high-entropy alloy with a single face-centered-cubic phase, Al_0.1CoCrFeNi, at elevated temperatures are studied to explore the high temperature performances of high-entropy alloys. Tensile tests at a strain rate of 10⁻⁴ s⁻¹ are performed at different temperatures ranging from 25 to 700 °C. While both yield strength and ultimate tensile strength decrease with increasing temperature, the maximum elongation to fracture occurred at 500 °C. Transmission electron microscopy characterizations reveal that, at both 25 and 500 °C, most of deformation occurs by dislocation glide on the normal face-centered-cubic slip system, {111}〈110〉. In contrast, numerous stacking faults are observed at 600 and 700 °C, accompanied by the decreasing of dislocation density, which are attributed to the motion of Shockley partials and the dissociation of dislocations, respectively. According to the Considere's criterion, it is assumed that the dissociation of dislocations and movement of Shockley partials at higher temperatures significantly decreases the work hardening during tensile tests, promoting the early onset of necking instability and decreasing the high-temperature ductility.