Transformation textures in pure titanium: Texture memory vs surface effect

Abstract

Surface effect-induced phase transformation heat treatment is performed on cold-rolled commercial pure titanium sheet to change and control the transformation texture. The results show that the type of final transformation texture changes from the texture memory effect type texture of TD-split basal to the surface effect type texture of 〈11−20〉//ND with the increase of heating temperature in helium atmosphere. At a low heating temperature of 920 °C and 1000 °C, the textures in sheets exhibited texture memory effect, while in the high heating temperature of 1100 °C, it showed the effects of both anisotropy in elastic modules of HCP titanium crystals and transformation strain. During the cooling phase, the surface effect can promote the preferred nucleation of α-phase grains on the plate surface, and then grow to the center layer of sheet along the ND direction. In the process of preferential nucleation of surface grains, texture memory effect and surface effect are a competitive process. The result of competition often shows that the small grains with tilted basal orientation (red) and cylindrical orientations (blue-green) are nucleated on the surface together, and the grains with blue-green orientation have the advantage of growth, leading to different grain morphology and microstructure. In addition to heating temperature and protective atmosphere, the degree of recrystallization before phase transformation also significantly affects the type of transformation texture. These differences in transformation texture and microstructure are explained according to the mechanism changes of the factors influencing the variant selection.