Phase stabilities and equilibria of the Ti-Al-Nb ternary system at intermediate temperatures III: The 1010 C isothermal section and Scheil reaction map

This paper is a continuation of our recent publications Xu et al. (2022, 2023). We systematically characterise the diffusion multiples using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD), and construct the whole composition range of the 1010 degrees C isothermal section in this work. There are nine stable phases, six three-phase regions and fifteen two-phase regions in the 1010 degrees C isothermal section. The beta o phase is in contact with the beta phase in the 1010 degrees C isothermal section. Two phase reactions occur between 1010 degrees C and 980 degrees C. The O phase is formed by the beta o+ sigma -> O reaction at a temperature of 997.5 degrees C, and an invariant reaction of beta + beta o ->alpha 2 +O occurred at a little above 980 degrees C. Based on our prior phase diagram works and the present work, we finally constructed the Scheil reaction map from the liquid phase down to 900 degrees C. These phase diagram and reaction works are mandatory for TiAl based alloys' design and application, and provides essential raw data to re-optimise the Gibbs free energy descriptions of this ternary system.(c) 2023 Elsevier B.V. All rights reserved.