Transition from ductilizing to hardening in tungsten: The dependence on rhenium distribution

Mechanical responses of tungsten (W) and its alloys are strongly controlled by the properties of 1/2<111> screw dislocations. Rhenium (Re), as a typical alloying and transmutation element in W, can substantially modify the properties of the dislocations, thus the plasticity of the materials. In this study, we investigate the interaction of Re and Re clusters with the screw dislocations in W by first-principles calculations in combination with theoretical models. Specifically, we propose two competing and Re-distribution dependent mechanisms, i.e. "ductilizing effect" and "hardening effect"; both are crucial to the mechanical properties of W. For the ductilizing effect, dispersed Re atoms weaken the surrounding interatomic interaction and reduce the shear resistance, thus facilitating the motion of the dislocation. In contrast, for the hardening effect, Re clusters formed by aggregated Re atoms due to irradiation can increase the Peierls stress and energy, thus hindering the motion of the dislocations. The proposed mechanisms shed light on the experimental observations that there is a Re-induced transition from ductilizing to hardening due to irradiation. The current work provides a theoretical guidance to the development of W-based future fusion materials in search of ductilizing alloying elements.