Abstract: Effects of different heating temperatures, cooling rates and holding time on microstructure and strengths of 8 mm thick TC4 titanium alloy plate were studied. The results show that the heating temperature significantly affects the microstructure and strength of the TC4 titanium alloy plate. The recrystallization occurs and the α phase tends to be equiaxed when the heating temperature increases from 800 ℃ to 850 ℃, resulting in the strength decreasing, the fraction of equiaxed α increases, the size and content of β phase increase where a small amount of α′ phase precipitated inside when the heating temperature reaches 900 ℃, resulting in the strength increasing. When the cooling rate is higher than 10 ℃/s, the martensitic transformation occurs, and the faster the cooling rate, the greater the trend of martensitic transformation and the higher the strengths. When the holding time increases from 180 s to 600 s, the yield strength and tensile strength increase by 6.1% and 7.9%, respectively, and when the holding time further increases to 900 s, the strength increment is small.

Key words: TC4 titanium alloy, heat treatment, microstructure, strength