Spheroidization behavior of (TiB+TiC+Y2O3)/α-Ti alloy during annealing

Abstract

In present study, the microstructure evolution and spheroidization behavior of (TiB+TiC+Y2O3)/α-Ti composite annealed at various temperatures and times were investigated. Results show that the volume fraction of αp is characteristic of S-type curve with the largest change rate in the range of 960–980 ℃. The mean length of αp lamellar is characteristic of Doseresp function, that is, the change rate decreases gradually as temperature increases. In the early stage of annealing, the spheroidization mechanism is associated with boundary splitting, which is controlled by the density of defects. When the heat treatment is prolonged, the spheroidization is completed by termination migration and Ostwald ripening. Owing to the heterogeneous geometrical orientation, crystallographic orientation, and (TiB+TiC+Y2O3), the spheroidization behavior is heterogeneous that is demonstrated by different spheroidization response of kinked and elongated α colonies. A positive spheroidization behavior is observed in particle-rich region, while a relatively negative spheroidization behavior is observed in particle lean region. The reinforcements hindered the dislocations movement and promoted spheroidization, thus, leading to the heterogeneous deformation and spheroidization. Furthermore, it could promote non-uniform nucleation to form remarkable random αs and αp texture, which gave a new inspiration to avoid “Macrozone”.