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

Abstract 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 α + β + γ at 1300 °C and the tie line of the α and β phases at 1400 °C were identified using electron probe microanalysis (EPMA). Neither the phase equilibria of the α, β and γ phases at 1300 °C nor the tie line of the α and β phases at 1400 °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 + β → β → α + β → α + β + γ → β + γ (The β phase and the B2 phase were not differentiated in the present paper.) The phase transformation temperatures were also measured by differential scanning calorimetry (DSC).