Effect Of High Energy Shot Peening On Structure And Properties Of Pure Titanium And Enhancing Bioactivity

In order to modify the stress shielding which is caused by the different elastic modulus between the replacer and the bone and improve the biocompatibility of pure titanium, a nano-gradient layer whose grain size decreased from top-surface to matrix was prepared by high energy shot peening(HESP) on commercial pure titanium. The effect of high energy shot peening on structure and properties were studied. Besides, post treatment was used to further improve the bioactivity. The mechanism of inducing apatite was analyzed. The main conclusions were drawn as follows:(1) A nano-gradient layer whose grain size decreased gradually from the surface to the matrix was obtained by high energy shot peening. On the top surface, the microhardness increased while the elastic modulus decreased of 17%. With the increasing of the peening time, the grain size decreased which led to the improvement of surface microhardness and tensile strength, but had an adverse effect on elongation and plasticity.(2) The corrosion resistance and surface hydrophilicity of the specimens decreased after HESP process. After soaking in SBF, titanium dioxide and calcium hydrophosphate were more easily to deposite on the HESP substrate. Although nanostructure enhanced the chemical reactivity of the Ti substrate, but the bioactivity as well as the deposition ability of apatite on the surface was still poor.(3) Alkali treatment not only enhanced the surface wettability, but also accelerated the deposition rate and shorted the forming time of apatite, which showed a significant improvement of bioactivity. The substrate after HESP for 45min performanced the best bioactivity with accelerating the element diffusion capacity and the deposition rate of apatite. Since the roughness of Ti increased after HESP, the cohesion between the substrate and the coating improved. Compared with alkali treated samples, the grain size of HESP specimens increased to 20μm after alkali-heat treatment, which decreased the deposition rate of apatite and displayed the lower apatite-inducing capability.