Phase stabilities and equilibria of the Ti-Al-Nb ternary system at intermediate temperatures II. The 980 °C isothermal section and reactions

Abstract

This paper is a continuation of our recent publication [S. Xu, et al. Journal of Alloys and Compounds 900 (2022) 163399–163407]. We systematically characterized the diffusion multiples using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM) and constructed the whole composition range of the 980 °C isothermal sections. The constructed range includes nine stable phases, twenty two-phase regions and ten three-phase regions at 980 °C. Six phase reactions occurring between 900 °C and 980 °C were determined. The ωo phase was formed by the βo+ γ→ωo reaction at a temperature just below 980 °C. The βo phase vanished through the βo→α2 + ωo+O reaction at a temperature just above 900 °C. These experimental results will bridge the existing research gap by providing the missing thermodynamic data. We believe that accurate predictions of phase diagrams and reactions occurring at intermediate temperatures using the obtained data are now feasible and the recomputations will resolve previous inconsistences and disputes.