Phase selection and solidification path transition of Ti-48Al-xNb alloys with different cooling rates

Ti-48Al-xNb alloys were solidified by containerless electromagnetic levitation with quenching system of the conical copper mold.The influence of cooling rates on phase selection of T1-48Al-xNb alloys was investigated.In near-equilibrium solidification condition,the dendrite βphase is observed as the leading phase.No other metastable phase(e.g.,α phase) is observed.In contrast,in rapid solidification condition,the metastable α phase is observed in as-quenched Ti-48Al-2Nb alloy.Furthermore,the metastable α phase is replaced by the primary β phase with Nb addition increasing.For Ti-48Al-(x=4,6,8)Nb alloys,increasing cooling rate results in a solidification path transition.The peritectic reaction(L+β→α) is therefore significantly suppressed.The relationships between primary dendrite arm spacing(λ_(1)) and cooling rate(τ) can be described.