Mechanical Properties and Microstructure Evolution During Bending–Unbending Deformation of Pure Titanium Sheet

In this study, the pure titanium sheets with thickness of 1 mm are deformed 1-5 times in the form of bending–unbending cyclic deformation. The bending angles before and after unbending are 120° and 180°, respectively. Mechanical properties of samples during cyclic deformation, including \(M /(BH)^{2}\)-surface strain curve and spring back in each bending cycle, have been investigated. Moreover, the twinning/detwinning behavior and texture evolution in three typical bending layers (i.e., the tensile layer, neutral layer and compressive layer) in cyclic deformation have been tested by EBSD and TEM, and analyzed systematically. The results indicate that the most intensive twins, consist of similar proportion of tensile and compressive ones, distribute in the inner layer after 1st bending. While they disappear almost entirely after 1st unbending. The twins in outer layer could also be detwinned, and the new twins could be activated during 1st unbending. Besides, the twin density increases obviously and the residual twins could not be detwinned clearly after multiple passes of cyclic deformation. Moreover, the Schmid factor along the \(\sigma_{2}\) direction functions in the activation of twin variants regardless of the three-direction stress states.