Effects of Surface Nano-crystallization on Tensile Properties of Commercial Pure Titanium

A nano-structured surface layer was obtained on the surface of CP-Ti by surface mechanical attrition treatment(SMAT),and the nano-structured surface of the SMAT sample was analyzed by means of X-ray diffraction(XRD),scanning electron microscope(SEM) and high-resolution electron microscope(HRTEM).The tensile properties of bulk Ti and nano-crystalline Ti processed by SMAT were studied.The results of tensile tests indicate that the surface nano-crystallization leads to an increase in yield strength and ultimate tensile strength and a decrease in uniform elongation compared with as-received ones.After SMAT,the grain size trends to increase from the surface to the initial part,and the fracture mechanism is also different among the nano-structured surface layer,submicro-fine grained layer and the coarse grain layer.The fracture in the nano-structured surface layer and submicro-fine grained layer is mainly gliding fracture,but that in the coarse grain layer is mainly dimple fracture.