Effect of high strain rate on the hot deformation behavior and microstructural evolution of dual-phase NiAlCrFeMo high-entropy alloy

Dynamic impact tests were conducted on the Ni₆₁Al₁₇Cr₁₀Fe₁₀Mo₂ high-entropy alloy (HEA) using a Split Hopkinson Pressure Bar at 25, 350, and 700 °C under strain rates of 3000, 3500, and 4000 s⁻¹. Microstructural evolution and deformation behavior were characterized by x-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Under high strain-rate loading, no continuous flow softening was observed, and the stress rapidly increased to above 800 MPa in the elastic region. At 4000 s⁻¹, the yield strength reached a maximum of 1056.64 MPa at 700 °C. The yield strength exhibited temperature and strain-rate-dependent strengthening. Yield strength decreased with increasing strain rate at 25 °C but increased at 350 and 700 °C. High strain-rate deformation resulted in more significant dislocation entanglement compared with low strain-rate thermal compression. At 25 °C, plastic deformation was dominated by pronounced dislocation accumulation. At 350 °C, thermal activation promoted partial dynamic recovery and incipient dynamic recrystallization (DRX). At 700 °C, extensive DRX accompanied by crystallographic orientation and texture evolution effectively accommodated dislocations and relaxed internal stresses. This study provides new insights into the temperature-dependent strengthening mechanisms of HEAs, which is valuable for the design and development of advanced materials for extreme environments.