Processing of NiTi shape memory sheets – Microstructural heterogeneity and evolution of texture

• Evolution of microstructure and texture in NiTi sheets during hot and cold rolling.
• Hot rolled sheets exhibit a strong through-thickness texture heterogeneity.
• This heterogeneity results from a temperature gradient during hot rolling.
• Cold rolling promotes a homogeneous {111} γ-fiber texture.
• Comparison of the textures with simulations reported in the literature.

In the present paper we study the evolution of microstructure and texture during processing of Ni51Ti49 shape memory sheets using electron backscatter diffraction. Hot rolling results in a heterogeneous microstructure which reflects a temperature gradient in the sheet. Equiaxed and randomly oriented grains are observed close to the surface of the hot rolled sheet while the sheet interior shows a strong texture containing two main texture components {111}<110> and {110}<110> with grains elongated along the rolling direction. In contrast, cold rolling in combination with a recrystallization heat treatment produces a more homogeneous microstructure in terms of grain morphology and grain size. It also promotes a random grain orientation along the rolling and transverse directions while the normal direction shows a strong γ-fiber {111} texture. To get a better understanding of the elementary deformation mechanisms which control the texture evolution during rolling, textures assessed in the present study are compared with simulations reported in the literature.