Microstructure evolution of the transitional region in isothermal local loading of TA15 titanium alloy

The microstructure of the transitional region determines the performance of TA15 component under isothermal local loading forming. To understand the characteristic of microstructure evolution in transitional region, a set of analogue experiments for isothermal local loading were designed and carried out to investigate the microstructure development under different temperatures and complex strain path. It is found that the isothermal local loading does not change the microstructural composition of TA15 alloy with initially equiaxed microstructure in the transitional region, though a small fraction of lamellar α phases appear at temperatures above 950 °C due to reheating and small deformation in the second loading step. Recrystallization takes place in the β matrix but not in the primary equiaxed α phases. The β grains are fine and equiaxed irrespective of strain path due to recrystallization. The existence of lamellar α refines the β grains. Kinked and disordered primary equiaxed α phases are produced under complex strain path. The grain size of primary equiaxed α phases increases slightly due to static coarsening and strain induced grain growth in multi-heat processing. The volume fraction of primary equiaxed α phases is not influenced by strain path but determined by working temperature.