Investigation of the phase transformations in Ti-22Al-25Nb alloy

In this paper, changes in the morphology and composition of the O, alpha 2 and B2/beta phases and the transformation relationship between the three phases of Ti-22Al-25Nb alloy were systematically investigated by performing a series of short heat treatments. The results showed that the phase transformations can be divided into three stages in the temperature range of 870 degrees C similar to 1080 degrees C. In the first stage of 870 degrees C similar to 930 degrees C, the O phase started transferring to alpha(2) + B2 first along grain boundaries with lamellar morphology due to short-range diffusion, and the O -> alpha(2) + B2 reaction was accompanied by a large amount of Nb segregation. With the increase in temperature, the phase transformation migrated from the boundaries to the inside of the grains, and the alpha(2)-phase spheroidized gradually. In the second stage from 960 degrees C to 1020 degrees C, granular alpha(2) and B2 phases precipitated directly from the O phase due to long-range diffusion. At 1020 degrees C, the O -> alpha(2) + B2 transition was completed and the granular alpha(2) phase mainly populated along the grain boundaries. In the third stage above 1020 degrees C, the main phase transformation was alpha(2) -> B2, and the aggregation and growth of the alpha(2) phase were observed in alpha(2)-rich regions. (C) 2016 Elsevier Inc. All rights reserved.