Dynamic mechanical properties and microstructure evolution of high-entropy alloy Al0.3CoCrFeNi: Effects of strain rate, temperature and B2 precipitates

Abstract

The mechanical properties and microstructural evolution of solution-treated and aged Al_0.3CoCrFeNi high-entropy alloys (HEAs) are systematically explored. The solution-treated alloy exhibits a single face-centered cubic (FCC) phase, whereas the aged alloy displays striped B${}_2$ precipitate bands rich in Al and Ni. Uniaxial compression tests are conducted in a strain rate range of 10^-3–2700 s⁻¹ and a temperature range of 173–693 K for both types of the alloys. At a constant temperature or strain rate, yield strength increases with increasing strain rate or decreasing temperature. The aged alloy demonstrates a slightly higher yield strength due to the presence of B${}_2$ precipitates giving rise to precipitate strengthening and enhanced deformation twinning. The investigation reveals multiple deformation mechanisms in both alloys, including dislocations, stacking faults, immobile Lomer-Cottrell locks, kink bands and deformation twins. Dislocations are along the {111} slip planes in the solution-treated alloy in contrast with tangled dislocations in the aged alloy. Besides, B${}_2$ precipitates, lower temperatures or higher strain rate all facilitate the activation of deformation twinning. Additionally, a modified Johnson-Cook-Cowper Symonds (JC-CS) constitutive model is developed, effectively capturing the plastic flow behavior of both alloy types across a broad range of strain rates and temperatures.