Effects of annealing heat treatment on grain boundary orientation differential evolution of TA15 alloy

The evolutions of grain boundary orientation differential of TA15 alloy after annealing heat treatments at different temperatures were investigated by EBSD and TEM. The results show a few small-angle grain boundaries of TA15 alloy transformed into large-angle grain boundaries when annealed at 800°C; more grain boundaries with large angle appeared greatly while annealed at 950°C; the average thermal activation energy was 151.4 kJ/mol for the transformation from small-angle grain boundaries to large angle grain boundaries, which is equal to the self-diffusion activation energy of α-Ti; it means that the transformation from the small-angle grain boundaries to the large-angle boundaries was controlled by the self-diffusion of titanium atoms. TEM micrographs show sub grain boundaries transformed into dislocation net with hexagonal net at the annealing temperature of 800°C, while lots of equiaxed grains were obtained after annealing treatment at 950°C.