B2 phase precipitation behavior in Ti–40Al–8Nb alloys during the hot deformation process

Abstract

In this work, the B2 phase precipitation behavior in Ti–40Al–8Nb alloys with a (α2+γ) duplex microstructure during the hot deformation process was investigated. Results showed that even if the deformation temperatures, 1000 °C and 1050 °C, were much lower than the B2 phase precipitation temperature (1160 °C), obvious B2 precipitates were observed in the compressed samples. The characteristics of B2 precipitates were significantly dependent on the deformation condition, i.e., its grain size and phase content increased with the rise of deformation temperature and decrease of strain rate. The detailed analysis indicated that the B2 phase was derived from the α2→B2 phase transition under the mechanical-thermal coupling effect. The applied stress provides a driving force for the redistribution of Nb element in the deformed α2 phase and the preferable thermal conditions with an enhanced diffusion accelerate the enrichment of Nb element in local regions. Moreover, the precipitated B2 phase was thermodynamically unstable, and an inverse transition B2→α2 occurred during the post-annealing at 1050 °C.