Grain Growth and Texture Evolution during Annealing of Submicrocrystalline Titanium Produced by Severe Plastic Deformation

Abstract

The paper considers the structure evolution during annealing of submicrocrystalline (SMC) titanium with a mean grain size of 0.2 µm, processed by severe plastic “abc” deformation. Electron microscopic studies have revealed that the microstructure of the SMC titanium is heterogeneous and of a mixed type. One can observe a high density of dislocations, grains, subgrains, elements of a banded structure and areas comprising coarse (up to 1-2µm) and fine (up to 0.1µm) grains. The grain boundary misorientation spectrum is presented by low angle and high angle boundaries of random and special types. Three stages of annealing of SMC titanium have been revealed. The second stage is connected with the intense SMC grain growth and the value of activation energy of grain growth at this stage is twice less than the value of activation energy of grain boundary diffusion in titanium. The latter is caused by acceleration of diffusion processes at SMC grain boundaries having an atom-disordered structure. The texture evolution with annealing temperature is characterized by weakening of predominantly basal texture in the as-received SMC state and strengthening of a prismatic component. The weakening of the basal component is connected with the growth of SMC grains first of all, as well as the increase of the volume fraction of special boundaries.