Biomedical Titanium And Titanium Alloy Powder Metallurgy Process

Titanium and its alloys are attractive for use as implantable materials due mainly to their excellent properties, such as low Young's modulus values, non-toxic, corrosion resistance and biocompatibility. However, high alloy cost restricts their employment to the biomedical field. The powder metallurgy technology has proven to be an excellent tool for the near net-shape fabrication of surgical implants, which combines near net shape and low production costs, especially for manufacturing complex shaped components, probably less expensive.In particular, T-13Nb-13Zr is a new, advanced, lower modulus of elasticity (modulus closer to bone) and high biocompatibility, quite attractive for employment as biomaterials. So this alloy is a promising candidate for medical use. In this research, the production of CP-Ti, Ti-6A1-4V and Ti-13Nb-13Zr alloys by employing a new powder metallurgy technology, which used titanium, niobium and zirconium hydride powders rather than conventional metal powders, have been developed. The dehydrogenation and sintering were carried out in one single process.The dehydrogenation processes of hydrides, densification process, microstrucure and mechanical properties of PM pure Ti, Ti-6Al-6V and Ti-13Nb-13Zr alloys were investigated by means of thermal dilatometer, thermal gravimetric analyses (TGA) and differential scanning calorimetry (DSC) analysis, X-ray diffraction(XRD) and scanning electon microscopy(SEM).Firstly, in order to optimize the dehydrogenation process and provide the theoretical basis of dehydrogenation-sintering process, the thermodynamics and kinetics of the decomposition of titanium, niobium and zirconium hydride powders were conducted. The temperature range of TiH2, NbH and ZrH2dehydrogenation are450℃-650℃,400℃-550℃and650℃-800℃respactivly.The dehydrogenation process of TiH2green compact can be described by shrinking unreacted-core model. The thickness of the titanium product layer increased, and the core of solid reactant TiH2decreases gradually to disappear with increasing reaction time. The dehydrogenation experiments of TiH2green compact with different diameters are conducted at600℃by the thermal gravimetric analyses. The results show that, the dehydrogenation process of TiH2green compact is controlled by internal diffusion. Therefore, the relationship between conversion and time is obtained for the dehydrogenation of TiH2green compact: t＝r0-—1.47[-x-(1+x)lh(1-x)]On the basis of the TG-DSC dehydrogenation characteristic analysis for titanium, niobium and zirconium hydrides and dehydrogenation experiments at low temperrature, subsequent dehydrogenation processes were carried out at650℃for1hour for the preparation of pure titanium and Ti-6A1-4V alloy, and at650℃for1hour,800℃for30min for Ti-13Nb-13Zr alloy to remove hydrogen, respectively. Considering the effect of sintering temperature and time on relative density and grain size of the sintered samples, the optimal sintering condition is1200℃/4h for pure Ti and Ti-6A1-4V alloy, and1300℃/4h for Ti-13Nb-13Zr alloy.The stable phase of pure Ti is equiaxed a structure at room temperature. The Ti-6A1-4V alloy samples show typical a+β microstructure, the microstructure consist of a platelets and the interplatelet β phase. Sintered Ti-13Nb-13Zr alloys consist of a typical Widmannstatten (a+β) microstructure, which is characterized by colonies of parallel a-plates embedded into a β-matrix. The tensile strength of pure titanium and Ti-6A1-4V alloy samples sintered at1200℃for4h reached680Mpa and989Mpa, respectively. The Ti-13Nb-13Zr samples sintered at1350℃for4h by powder metallurgy show satisfactory tensile strength, and the value reached1094MPa.The above results showed that, for the pure Ti, Ti-6A1-4V and Ti-13Nb-13Zr alloys sintered directly from hydride powders by powder metallurgy, relative density can reach98%. All tensile strength exceeded standard; All the elongation and reduction of area are very low. For pure Ti and Ti-6A1-4V alloy by extrusion and swaging processing, tensile strength decreased, and the plasticity is improved. The elongation can reach30%and16%, repectively. Thus, as a result, the produced pure Ti and Ti-6A1-4V alloy have comparable or better mechanical properties than that made by traditional wrought metallurgy method in GB/T2965-2007stantard. It can be concluded that the hydride powder method route with near-net-shape processes is reasonable and feasible for production of titanium and its alloys for biomedical applications.