In-situ study of anisotropic strain-hardening and grain boundary mediated deformation in commercially pure titanium

Abstract

In this study, we investigated the anisotropy in tensile deformation behaviour of CP-Ti plate in the rolling (RD) and transverse direction (TD), using in-situ SEM-EBSD testing and stress-relaxation method. The EBSD-assisted slip trace analysis was conducted to examine the slip systems activated within individual grains. It was found that the prismatic slip is dominant in the RD sample, whilst the activity of non-prismatic slip systems is higher in the TD sample. The slip transfer significantly occurred in the TD sample, thereby promoting the activity of multiple slips and dislocation interactions at the grain interiors. However, the limited occurrence of slip transfer in the RD sample indicates the strong dislocation pinning at the grain boundaries (GBs). Combined with the EBSD analysis, the SEM observations revealed that the GBs with ledge character are formed in the slip-favourable and -unfavourable grain pairs, and the GBs with sink character are created in the grain pairs whose c-axes are equally inclined to the loading direction, but the sign of c-axis inclination angles is opposite with each other. The formation of GB ledges and GB sinks was pronounced in the RD and TD sample, respectively. The GB-dislocation interactions and GB-mediated deformation arising from the orientation relationship between the particular grain pairs led to the anisotropy in strain-hardening behaviour of polycrystalline α-Ti.