The effect of heat-treatment on micro structure and texture evolution in Ti-6Al-4V alloy and its effect on room temperature tensile properties and deformation mechanism
Ti-6Al-4V, an α+β titanium alloy, is widely used in the aerospace industry due to its excellent properties such as high strength-to-weight ratio, good corrosion resistance, formability and excellent medium temperature capabilities. The Ti-6Al-4V alloy was received as a hot-rolled bars, having initially a bimodal microstructure. It was heat-treated to produce three different microstructures (Lamellar, Equiaxed and Bimodal). A variation in phase fraction (α / β phase fraction) and morphology was achieved by altering soaking temperature and cooling rate. β-treatment (1050°C/1hr/Air Collinig) of hot rolled structure resulted in lamellar microstructure. A further variation of microstructures i.e. equiaxed and bimodal was achieved by varying the soaking temperature (900°C and 950°C, 4 hours soaking time) followed by furnace cooling and air cooling respectively. The dimensions and volume fraction of microstructural constituents were measured using quantitative stereology. As α phase is the major constituent of all the microstructures , electron backscatter diffraction (EBSD) technique was employed to investigate the orientation and distribution of α phase. Transmission electron microscope (TEM) was used to characterize the evolution of dislocation substructure in α grains which formed due to recrystallization and strain associated with β to α transformation . Room temperature tensile test was conducted for as received (hot rolled) as well as heat-treated microstructures to correlate the effect of microstructural variations with mechanical properties. Scanning electron microscope was used to understand failure mechanism. EBSD technique was used to characterize strain localization and neighbouring grain orientation. A detailed study of dislocation interaction in α phase was carried out using TEM.