Microstructure Evolution and Mechanical Property of TC25G Titanium Alloy During High Temperature Deformation

Microstructure evolution of TC25G titanium alloy bar with basket microstructure after different deformation degrees was studied and the changes of its thermal stability and creep resistance at 550 degrees C were compared. The results show that the tensile plasticity after thermal exposure increases and the creep resistance decreases with the increase in deformation degree. The plasticity and creep resistance match well at 100% deformation degree and can meet the requirements of engineering application. The increase in deformation degree corresponds to the spheroidizing process of lamellar alpha phase. Before the lamellar alpha phase is fully spheroidized, the interface strengthening effect of multi-layer structure makes the alloy have good creep resistance at high temperature. However, after alpha-phase spheroidization, the alloy has better plasticity because of the microstructure dominated by equiaxed microstructure. With the increase in deformation degree, the size of the fracture dimples becomes smaller and more uniform, and the dimple depth increases, which indicates that the plasticity after thermal exposure increases. The results of nano-hardness test show that the microhardness of primary alpha phase is higher than that of beta transforms, and the creep resistance can be improved by adjusting the content and distribution of alpha phase in the alloy by solution temperature. The extent of lamellar alpha phase spheroidization can be controlled to obtain the best matching of strength and plasticity at high temperature.