Grain size and specimen thickness effects on twinning behaviors in high strain rate deformation of ultra-thin pure titanium sheet

Identifying grain size and specimen thickness effects on the twinning characteristics and texture evolution of ultra-thin pure titanium sheet is essential for its extensive applications in many industries. In this research, ultra-thin pure titanium sheet with different grain sizes and thicknesses were deformed to different strains by electromagnetic-assisted bulging. Then the deformation twins were analyzed on a grain-by-grain basis to determine both the volume fraction of twins and the Schmid factor of twin variants in each grain. Results indicate that twin density of ultra-thin pure titanium sheet decreases when sample thickness decreases from 205 μm to 45 μm. Moreover, deformation twinning can be promoted when grain size increases from 7.5 μm to 27.4 μm but also can be restricted to a certain extent when grain size increases to 38.2 μm. In addition, grain size plays an evidently positive effect on multiple twin variants activation so as to affect the misorientation distributions. Furthermore, the frequency of twin variants with lower Schmid factor decreases with the increase of grains size from 7.5 μm to 38.2 μm. This is well explained by the strain accommodation criterion. By affecting the deformation mechanism of ultra-thin pure titanium sheet, size effects also play significant roles in the texture evolution.