Nonuniform Recrystallization and Growth Behavior of Grains Dominated by Grain Misorientation and Interfacial Energy in Metastable β Titanium Alloy

Metastable titanium alloys usually exhibit nonuniform grain growth behavior under solution treatment, resulting in black spots with dimension of millimeter or centimeter. In this paper, the nonuniform recrystallization and growth behavior of grains were studied in the Ti-5Al-5Mo-5V-1Cr-1Fe metastable titanium alloy. Electron backscatter diffraction technique was used to characterize the crystallographic orientation after solution in both the normal and abnormal (black spot) macroscopic regions, containing grains with high misorientation angles (>10 deg) and subgrains with low misorientation angles (<10 deg), respectively. The nonuniform growth behavior of grains in the abnormal regions was clarified based on the following two aspects: (1) grain recrystallization and growth inside the abnormal region were delayed due to the low-accumulated plastic strain and low-angle subgrain boundaries; and the growth of some subgrains with favorable neighboring region was accelerated with the transition from low-angle subgrain boundary to high-angle grain boundary; (2) with enough holding time at the phase region, the abnormal region was consumed via the normal grains growing inside. The migration of grain boundaries with various orientations depends on the interfacial energy, which is relevant to the misorientation angle and the interfacial plane between the neighboring grains.