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 (alpha + beta) 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 degrees C) followed by oil quenching (OQ), air cooling (AC), and furnace cooling (FC), respectively. Primary alpha (alpha(P)) and secondary alpha (alpha(S)) were dominant in the microstructure, when heat-treated below beta(T) (beta-transus) temperature, i.e., 850 and 930 degrees C. Widmanstatten alpha (alpha(WS)) and basket-weave alpha (alpha(BW)) were dominant features in the microstructure of the samples heat-treated above the beta(T), i.e., 1066 degrees C. Formation of the martensite (alpha ') was observed in all three cases of the OQ samples. Differences in the volume fraction of the alpha(P) and alpha(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 beta(T) which shows the dependence of the texture on the volume fraction of alpha(P) and alpha(S). Similarly, formation of the big alpha colonies causes the changes in the texture when heat-treated above the beta(T). Grain partitioning of alpha(P) and alpha(S) in 850 and 930 degrees C-OQ samples shows a similar type of the texture for both the phases, difference being in the intensity of the texture fibers. Martensite (alpha ') formation during OQ increased the microhardness, whereas coarsening of grains during FC decreased the microhardness of the samples. There was similar to 23% variation in the modulus of elasticity (E), which depended on the heating temperature and cooling rate.

Automated summary

The microstructure, texture, and mechanical properties of heat-treated two-phase titanium alloy samples were investigated. Different heating temperatures and cooling rates resulted in variations in the volume fraction of different phases and texture intensity. The formation of martensite during oil quenching increased microhardness, while grain coarsening during furnace cooling decreased microhardness. The heating temperature and cooling rate also significantly affected the modulus of elasticity.