Strength and ductility of niobium alloys with nonmetallic elements: A first-principles study

Nonmetallic elements C, H, N, O and Si which normally are introduced into the metallic matrix unintentionally, usually have significant effects on the mechanical properties of alloys, which, however, is unclear for niobium. Hardness and ductility are two important properties for alloys, which can be characterized by the unstable stacking fault energy γus and the ratio between surface energy γs and γus, respectively. In this study, by using first-principles calculation, we find that C, N, O and H decrease the hardness and ductility of niobium. On the other hand, minor alloying of Si in niobium can improve the hardness and show excellent ductilization capability.