MICROSTRUCTURAL EVOLUTION OF A HOT-ROLLED TI-40AL-10NB ALLOY

Microstructure of a Ti-40Al-1ONb alloy, which was processed by convent ional hot rolling, was investigated using optical metallography, scann ing electron microscopy (SEM), X-ray diffraction (XRD) and transmissio n electron microscopy (TEM). The microstructure of as-rolled Ti-40Al-1 ONb alloy consists of alpha(2)/gamma lamellar grains elongated along r olling direction and gamma-phase grains, all dispersing in a B2-phase matrix. During the hot rolling, continuous and discontinuous coarsenin g of alpha(2)/gamma lamellar structure occurs and produces a serrated grain boundary with B2-phase matrix. The microstructure of hot-rolled Ti-40Al-1ONb alloy after subsequent heat-treatment at the temperature range from 650 to 1400 degrees C was also examined. The Widmanstatten structure consisting of the alpha(2)/gamma lamellar laths may be obtai ned by heat-treating above beta transus temperature. By annealing at t he temperature of alpha(2) + beta/B2 two phase region, the microstruct ure is composed of equiaxed alpha(2)/gamma lamellar (or alpha(2)-phase ) grains and B2-phase grains. When the heat-treatment temperature is b etween 1000 and 1200 degrees C, the elongated alpha(2)/gamma lamellar grains tend to spheroidize, and the volume of gamma-phase increases. W hen the heat-treatment temperature is below 900 degrees C, the meta-st able B2-phase transforms into the omega-phase of B8(2) structure, and the gamma-phase is also found in B2-phase. (C) 1997 Elsevier Science S .A.