Dynamic tensile deformation and microstructural evolution of AlxCrMnFeCoNi high-entropy alloys

The influence of microstructure and strain rate on tensile behavior of AlxCrMnFeCoNi (x = 0, 0.4 and 0.6 in molar ratio) high-entropy alloys was investigated. The alloys with lower Al content exhibited microstructures of simple fcc solid solution whereas the Al0.6CrMnFeCoNi alloy consisted of fcc + bcc mixed solutions after thermomechanical processing. Al0.6CrMnFeCoNi showed higher tensile strength at quasi-static condition due to the combinative contributions from solution strengthening, grain-boundary strengthening and precipitation hardening. Under dynamic loading conditions, both the yield strength and work hardening increased remarkably with increasing strain rate for the two Al-containing alloys. However, the Al0.4CrMnFeCoNi alloy showed a larger strain-rate sensitivity than Al0.6CrMnFeCoNi alloy owing to the existence of abundant bcc phase and interphase boundaries. Johnson-Cook constitutive model can be utilized to describe the effects of strain rate and strain on the dynamic flow stress. Compared to quasi-static condition, the higher density dislocations and interaction were the main characteristics of microstructures for dynamic deformation, leading to the increased flow stress. High volume fraction of bcc phase and strain rate led to a transition from ductile to quasi-cleavage fracture.