Hardening Behavior in VNbTa Refractory Multi‐Principal Element Alloys Upon Helium Ion Irradiation

In this study, the VNbTa refractory multi‐principal element alloy (RMPEA) was selected as the model alloy for 180 keV He ⁺ ion irradiation experiments at various doses of 0.1 dpa, 0.5 dpa, 1 dpa, and 5 dpa, respectively. As the irradiation dose increases, the lattice parameter of VNbTa exhibits a fluctuating evolution of “contraction‐expansion‐contraction,” due to the competitive interaction between the relaxation of lattices and the evolution of defects due to ion irradiation. Nanoindentation were employed to characterize the irradiation‐induced hardening behavior. The contribution of irradiation defects to hardening is separated via an irradiation‐induced hardening model. The result indicates that as the dose increases, irradiation‐induced defects accumulate beneath the indenter, inhibiting dislocation motion and suppressing the expansion of the plastic zone. As the dose grows, the evolution of the fitting parameters is initially rapid but subsequently slows down, which may be attributed to the saturation of the defect number density. This study provides references for quantifying irradiation hardening in VNbTa RHEAs.