Microstructural evolution of a hot-rolled Ti–40Al–10Nb alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1997-12, Vol.239, p.694-701
• Main Authors: Yu, T.H., Koo, C.H.
• Format: Article
• Language: English
• Subjects: Coarsening; Hot rolling; Microstructure; Titanium aluminides
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(97)00654-0

Microstructure of a Ti–40Al–10Nb alloy, which was processed by conventional hot rolling, was investigated using optical metallography, scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of as-rolled Ti–40Al–10Nb alloy consists of α 2/ γ lamellar grains elongated along rolling direction and γ-phase grains, all dispersing in a B2-phase matrix. During the hot rolling, continuous and discontinuous coarsening of α 2/ γ lamellar structure occurs and produces a serrated grain boundary with B2-phase matrix. The microstructure of hot-rolled Ti–40Al–10Nb alloy after subsequent heat-treatment at the temperature range from 650 to 1400°C was also examined. The Widmanstätten structure consisting of the α 2/ γ lamellar laths may be obtained by heat-treating above β transus temperature. By annealing at the temperature of α 2+ β/B2 two phase region, the microstructure is composed of equiaxed α 2/ γ lamellar (or α 2-phase) grains and B2-phase grains. When the heat-treatment temperature is between 1000 and 1200°C, the elongated α 2/ γ lamellar grains tend to spheroidize, and the volume of γ-phase increases. When the heat-treatment temperature is below 900°C, the meta-stable B2-phase transforms into the ω-phase of B8 2 structure, and the γ-phase is also found in B2-phase.