Mechanical behaviors of irradiated FCC polycrystals with nanotwins

In this paper, a theoretical model is proposed to characterize the mechanical behaviors of irradiated face-centered-cubic (FCC) polycrystals with nanotwins. At the grain level, the spatial-dependent interactions among twin boundaries (TBs), irradiation-induced defects and dislocations are considered in the crystal plasticity model. At the polycrystal level, the elastic-viscoplastic self-consistent (EVPSC) method is applied to bridge the property of microscopic individual grains to macroscopic mechanical behaviors of polycrystals with nanotwins. Applications of the proposed model to nanotwinned (nt) copper show that the numerical results match well with corresponding experimental data. It is found that: without irradiation, the mechanical properties of nt metals are closely related to the loading direction with respect to the TBs and the width of twin spacing. There exists a critical twin spacing for nt polycrystals: above which, the impediment of slip dislocations due to TBs leads to the hardening mechanism; below which, the slip of partial dislocations along the TB planes becomes dominant and leads to the softening mechanism. With irradiation, the irradiation-induced defects acting as obstacles could impede the movement of dislocations, which leads to irradiation hardening. However, TBs can effectively absorb irradiation-induced defects and reduce the defect density. Therefore, the irradiation hardening effect may be weakened due to the effects of TBs. The proposed model may offer an effective theoretical method to study the mechanical behaviors of irradiated polycrystals with nanotwins.