Oxygen solutes-regulated low temperature embrittlement and high temperature toughness in vanadium

The plasticity of body-centered cubic (BCC) metals is sensitive to interstitial trace impurities. Owing to high oxygen affinity, vanadium (V) shows a tendency of embrittlement with increasing oxygen concentration. However, how oxygen solutes affect the ductile-to-brittle transition (DBT) behavior of V remains unclear. In this study, we investigate the DBT behavior of V with different oxygen solute concentrations using small-punch test. As oxygen content increases, the DBT temperature (DBTT) rises incrementally accompanied by a widening of the semi-brittle transition zone. The reduction of the lower fracture energy plateaus indicates a classical low-temperature embrittlement, while the rising of the upper fracture energy plateaus manifests a remarkable high-temperature toughening. Below DBTT, owing to the strong pinning effect of oxygen-vacancy complexes on dislocations, only a limited number of slip systems were activated with very low dislocation density , and all screw dislocations are immobile. Above DBTT, owing to the intensive interactions between dislocation and oxygen-vacancy complexes, frequent dislocation cross-slips trigger multiple slip systems and accelerate dislocation multiplication and storage, all of which contribute to the high-temperature toughness. These findings clarify the effect of oxygen solute on the DBT of V and guide the design of high-performance refractory metals.