Effects of Ti content on microstructure and phase compositions of Nb-Si based ultrahigh temperature alloy

Nb-Si based ultrahigh temperature alloys were prepared by vacuum non-consumable arc melting and the effects of Ti addition contents on their microstructure and phase composition were investigated. The results show that Ti addition contents could exert an obvious influence on the types, sizes and area fractions of primary (Nb,X)₅Si₃ in the microstructure. When Ti addition content is relatively low (0at%~10at%), the primary silicides are α-(Nb,X)₅Si₃ and its area fraction increases significantly with increase in Ti addition content. When the Ti addition content is ranged from 18at%~20at%, the primary silicides are of two types: α-(Nb,X)₅Si₃ and γ-(Nb,X)₅Si₃. However, the amount of α-(Nb,X)₅Si₃ decreases with increase in the Ti addition content in the alloy. When Ti addition content in the alloy varies from 22at%~30at%, there is only one form of primary silicides i.e., γ-(Nb,X)₅Si₃. Moreover, as the Ti addition content in the alloy increases, the size of α-(Nb,X)₅Si₃ increases while the size of γ-(Nb,X)₅Si₃ is less affected. In addition, as the Ti addition content in the alloy increases, Ti concentration in both Nbss and γ-(Nb,X)₅Si₃ increases while that in α-(Nb,X)₅Si₃ is lower and does not change obviously.