Quantitative metallography analysis of microstructure of BT25 titanium alloy deformed in two-phase field

The isothermal compression of BT25 titanium alloy with initial lamellar was carried out with four deformation degrees and the effect of deformation degree on microstructure parameters (volume fraction, thickness and globularization ratio of α phase) was investigated based on quantitative metallography. The results show that the process of α lamellar pinch-off/fragmentation takes place with increasing the deformation degree, which results in the decrease of the Feret ratio of α lamellar and the increase of globularization ratio. It reaches 85.23% when the deformation degree is 80%. The microstructure homogeneity of the alloy is improved. Mass diffusion from both ends of α lamellar to center happens during the deformation process, making the thickness of α phase increase (about 1.6 μm with increasing deformation degree from 0% to 80%). The volume fraction of α phase (about 60%) remains unchanged because of a stable deformation temperature. However, it decreases slightly in the case of high forging strains.