Abstract
NbSi-based alloy, which primarily consists of niobium solid solution (NbSS) and α-Nb5Si3, is a promising ultra-high temperature material. The overall fracture toughness of this alloy is limited by the brittle α-Nb5Si3 phase. Alloying Ti, which can improve the toughness of NbSS, is typically introduced into NbSi-based 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-Nb5Si3 is unclear, which makes the beneficial effect of Ti on the mechanical properties of NbSi-based 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 Nb5Si3 becomes 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 NbSi-based alloy.
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