Mechanical properties and biological responses of ultrafine-grained pure titanium fabricated by multi-directional forging

We aimed to investigate strengthening of pure titanium by ultra-grain refinement using multi-directional forging and to examine the biocompatibility after sulfuric acid treatment. Commercial titanium grade 2 was multi-directional forged to large cumulative strain to obtain homogeneous ultrafine-grained structure. The evolved microstructure of the obtained material was equiaxed and ultrafine-grained with high dislocation density. Average grain size was evaluated to be approximately 100 nm. The ultrafine-grained titanium showed higher tensile strength, Vickers hardness and a lower elastic modulus compared to conventional pure titanium grade 2. The surface features of the multi-directional forged titanium after acid treatments were characterized by a roughness of 1 mu m composed of equiaxed fine dimples with fractal structure and a hydrophilicity of 15. Cell proliferation on multi-directional forged titanium was significantly promoted than on conventional titanium. The above results demonstrated the high potential of multi-directional forged titanium as a superior biocompatible implant material.