Phase transformations and phase equilibria of a Ti-46.5Al-16.5Nb alloy

The isothermal sections of the phase diagram and the liquid projection of the Ti-Al-Nb ternary system as well as the phase transformations of a Ti-46.5Al-16.5Nb alloy were calculated using Pandat software. The solidification sequence and subsequent phase transformations of the alloy were verified by microstructural observations and thermo-analysis (TA). The tie-triangle of the three-phase region of alpha + beta + gamma at 1300 degrees C and the tie line of the a and beta phases at 1400 degrees C were identified using electron probe microanalysis (EPMA). Neither the phase equilibria of the alpha, beta and. phases at 1300 degrees C nor the tie line of the a and beta phases at 1400 degrees C are in agreement with the calculated phase diagrams reported in the literature. The solidification sequence and subsequent solid-state phase transformations of this alloy were determined as follows: liquid -> liquid + beta -> beta -> alpha + beta -> alpha + beta + gamma -> beta + gamma (The beta phase and the B2 phase were not differentiated in the present paper.) The phase transformation temperatures were also measured by differential scanning calorimetry (DSC). (C) 2016 Elsevier Ltd. All rights reserved.