Surface Roughness and Deformation of Grain during Tensile Plastic Deformation of Polycrystalline Titanium

The surface folds formed due to plastic deformation and the deformation behaviors of two kinds of polycrystalline titanium with grain sizes of about 30µm and 150µm respectively have been consecutively observed and measured by the scanning probe microscope. The results show that the surface folds in two kinds of specimens were increased with the increase of strain, but their relative position were kept unchanged during deformation. A large amount of twins were formed in each grain when the plastic strain reached about 0.1,which resulted in some new plastic folds. However, these new plastic folds had no influence on the positions of the plastic folds in both specimens as a whole. The roughness, the maximum height difference, and the averaged slope angle of the microscope surface profile increase with the applied tensile strain. But the surface roughness of the specimens with large grains are 1.4 to 4 times higher than that of the specimens with small grains. Two sudden changes in roughness could be observed in the specimens with large grains while the roughness in the specimens with small grains were kept smoothly increased. The influence of grain size on the plastic mechanism and surface roughness were discussed.