Toughening of α-Nb₅Si₃by Ti

Nb Si-based alloy, which primarily consists of niobium solid solution (Nb_SS) and α-Nb₅Si₃, is a promising ultra-high temperature material. The overall fracture toughness of this alloy is limited by the brittle α-Nb₅Si₃phase. Alloying Ti, which can improve the toughness of Nb_SS, is typically introduced into [Formula presented] alloy. The overall toughening effect of the alloying elements on multi-composites is dependent on the alloying effect on each component. However, the influence of Ti on the brittleness of α-Nb₅Si₃is unclear, which makes the beneficial effect of Ti on the mechanical properties of [Formula presented] alloy ambiguous. By calculating the ideal cleavage energy and cleavage strength using a first-principles method, we find that a low amount of Ti will improve the toughness of Nb₅Si₃, while Ti-rich Nb₅Si₃becomes more brittle, which is in good agreement with experimental results. The concentration-sensitive effect of alloying Ti is induced by the variation of its substitution site and can be well explained by the electronic structure analysis. Our findings demonstrate that the alloying amount of Ti should be carefully selected in the [Formula presented] alloy.