Nucleation behavior of ωo phase in TiAl alloys at different elevated temperatures

Abstract

In this study, the location, morphology and composition of the ωo phase, which transformed from B2 phase in Ti–45Al–8.5Nb-(W, B, Y) (at.%) alloy, were investigated by short-time heat treatments in an intermediate temperature range. The results showed that the characteristics of B2 → ωo phase transformation differ with the reduction in temperature. Below the ωo solves, the B2 → ωo phase transformation will take place within B2 area. There are existing two stages in the phase transformations during cooling from 850 to 700 °C. When the temperature is high (850 °C), granular ωo populated along the dislocations existing in B2 phase and B2 grain boundaries, due to higher energy and the enrichment of Nb element at the B2/γ boundaries. It is worth noting that only two ωo variants nucleate at 850 °C. With the decrease in temperature, the nucleation sites of ωo phase would be migrated from the B2 boundaries to the inner area. At the temperature of 700 °C, four ωo variants with different orientations nucleate homogenously within B2 grain. The ordered ωo formation process of Ti–45Al–8.5Nb-(W, B, Y) alloy during cooling was postulated in this study.