Investigations on the effect of heating temperature and cooling rate on evolution of microstructure in an α + β titanium alloy

In the present work, the effect of cooling rate on the evolution of the microstructure and mechanical properties of an α + β titanium alloy has been systematically investigated. Titanium alloy samples were heated to 1066 °C (above the β transus), 930 °C (just below the β transus), and 850 °C (well below the β transus) followed by oil quenching, air cooling, and furnace cooling, respectively. Primary alpha (αp), lamellar alpha (αL), and martensite (α′) were the dominant features of the microstructures for all the samples heated below the β transus. Furnace-cooled samples showed variation in the size and shape of the αpand fraction of αLaccording to the heating temperature. At slower cooling rates, the thickness of the αLincreased with the increase in temperature. Transmission electron microscopy and X-ray diffraction confirmed the presence of α′ in all the quenched samples. The volume fraction and size of the αpdecreased with the increase in temperature but was independent of the cooling rate. The microhardness was relatively unaffected by the cooling rate for heating just below the β transus, i.e., 930 °C. The modulus of elasticity was found to be extremely sensitive to the microstructure.