Correlation of Alpha Phase and Its Texture Stability in Heat-Treated Ti-6.5%Al-4.4%V-0.15%Fe Alloy

In the present work, microstructure, texture, and mechanical properties were investigated for the heat-treated two-phase (α + β) titanium alloy samples. Ti-6.5%Al-4.4%V-0.15%Fe alloy samples were heated to three different temperatures (850, 930, and 1066 °C) followed by oil quenching (OQ), air cooling (AC), and furnace cooling (FC), respectively. Primary alpha (α_P) and secondary alpha (α_S) were dominant in the microstructure, when heat-treated below β_T (beta-transus) temperature, i.e., 850 and 930 °C. Widmanstatten α (α_WS) and basket-weave α (α_BW) were dominant features in the microstructure of the samples heat-treated above the β_T, i.e., 1066 °C. Formation of the martensite (α′) was observed in all three cases of the OQ samples. Differences in the volume fraction of the α_P and α_S were observed in the microstructure due to differences in the heating temperature and cooling rate. Texture developments after heat treatment were measured through the electron back-scatter diffraction (EBSD) technique. Variation in the texture intensity values was observed in the samples heat-treated below the β_T which shows the dependence of the texture on the volume fraction of α_P and α_S. Similarly, formation of the big α colonies causes the changes in the texture when heat-treated above the β_T. Grain partitioning of α_P and α_S in 850 and 930 °C-OQ samples shows a similar type of the texture for both the phases, difference being in the intensity of the texture fibers. Martensite (α′) formation during OQ increased the microhardness, whereas coarsening of grains during FC decreased the microhardness of the samples. There was ~ 23% variation in the modulus of elasticity (E), which depended on the heating temperature and cooling rate.