Elastic and Plastic Microscopic Undulation on the Surface of Polycrystalline Pure Titanium Under Tension

Commercial pure titanium has been widely used in the aerospace, chemical, and biomedical industries because of its light weight, high corrosion resistance, high strength, high heat resistance, and good biocompatibility. Pure titanium takes the form of a hexagonal closed-pack structure with anisotropic elasticity and plasticity, with most of its components being polycrystalline aggregates having different crystal orientations. Small mechanical loading under elastic conditions therefore always induces inhomogeneous microscopic deformation, and the resulting inhomogeneity brings about various defects such as inhomogeneous plastic deformation, microcracking, and necking. It is therefore important to investigate the microscopic inhomogeneous deformation under elastic and plastic conditions. In this study, a plate specimen of commercial pure titanium was subjected to a tensile test on the stage of a digital holographic microscope (DHM), and the microscopic deformation of grains in the specimen under elastic and plastic conditions were observed and measured. During the test, the grains’ height distribution was measured in a fixed area on the specimen’s surface at each tensile loading step, and the correlation between height distributions at different loads was examined. We found from the measurements that each grain shows a different height change even under elastic conditions with a small load. This inhomogeneous height change was enhanced as the load was increased to plastic conditions. A strong correlation between the height changes under elastic and plastic conditions was also found. This result suggests that the microscopic deformation experienced under plastic conditions is predictable from that observed under elastic conditions.