Development of grain structure during friction stir welding of pure titanium

The microstructure evolution during friction stir welding of commercial purity titanium was studied. Material flow was found to be close to the simple-shear deformation and arose mainly from the prism slip. The grain structure evolution was shown to be a complex process including several stages. Far from the welding tool, the microstructural evolution was found to be governed by geometrical effects of strain and limited discontinuous recrystallization. In the stir zone, formation of a strong texture was shown to lead to texture-induced grain convergence, and the grain structure development was thus closely related to the texture evolution.