Anomalous solution softening by unique energy balance mediated by kink mechanism in tungsten-rhenium alloys

Abstract

Nucleation of transmutation products such as rhenium (Re) and osmium (Os) is a central issue contributing to changes in mechanical properties under neutron irradiation in fusion reactors. In particular, Re solutes in tungsten (W) not only affect hardening via radiation-induced precipitation but also have a notable softening effect. We explored the softening/strengthening behaviors of various solutes in a W matrix by density functional theory (DFT) calculations combined with a solid solution model. Our DFT calculations of the solutes show a clear trend in the interaction energy between different solutes and screw dislocations, which also influences the solid solution behavior. These predictions, based on a solid solution model and DFT calculations, reasonably reproduce the complex softening/strengthening behavior as a function of temperature and solute concentration. Notably, solutes such as Re have relatively weak attractive interactions and do not markedly influence the pinning effect; however, such solutes can reduce the energy barrier for kink pair nucleation. We conclude that this specific balance is the origin of macroscopic solid solution softening in dilute body-centered cubic alloys.