Effect of grain size on twinning behavior of pure titanium at room temperature

Abstract The grain size effect on deformation twinning behavior of pure titanium during uniaxial compression was investigated using electron backscattered diffraction (EBSD) technology. In this work, EBSD statistical analyses on big data sets of twins in pure titanium specimens with different initial grain sizes were carried out. Results show that a greater deformation coordination ability caused by small initial grains results in higher yield strength. Moreover, upon increasing the grain size, more twin variants were activated and more twin lamellae developed. The types of activated twins in specimens with larger grain size were more diverse. The twin growth of different twin modes was affected by grain size differently. The volume of the {10–12} extension twinning was sensitive to the grain size due to the small shear force generated by it per unit volume. In addition to grain size, grain orientation and the amount of deformation also significantly affect twinning activity during deformation. The primary twin lamellae were more abundant in the normal direction (ND) specimens as the deformation increased, while more lamellar thickening occurred in the rolling direction (RD) specimens. Because of more diverse primary twin modes in larger grains, the secondary twinning was also various. The secondary twinning {10–12}→{11–22} later developed. It is speculated that the activation of the secondary twins may be related to the volume ratio of the primary twin to the matrix grain. Simultaneously, the twin-twin interactions were more common in larger grains, restricting twin growth and promoting the material's hardening. The types and structures of twin-twin interactions in specimens with large grain size were also varied.