The Fabrication And Superelasticity Of Biomedical Porous Ti-Nb Based Alloys

The biomedical Ni-free porous Ti-Nb superelastic alloys can exhibit good superelsticity, like porous NiTi shape memory alloys (SMAs). Furthermore, they contain of non-toxic elements. Thus, the problem that the dissolved Ni ion is harmful to human body in porous NiTi SMAs can be solved ultimately. The porous Ti-Nb superelastic alloys can exhibit excellent biocompability, and they show great potential in biomedical applications. Thus, they become one of potential candides as biomedical materials. In this study, the porous Ti-Nb based superelastic alloys have been fabricated by conventional sintering (CS) method, and pre-treat the powder ball milling and then sintering it. The microanalysis approaches and thermomechanical anlaysis methods, such as XRD,SEM, DSC were employed to characterize the microstructure, pore characterisitics, mechanical properties and superelasticity.It is found that the porous Ti-Nb based superelastic alloys fabricated by CS consists ofαandβphases. With increasing of the content of Nb and Zr, the content ofβphases would increase. The porous Ti-22Nb-6Zr alloy is consist mainly ofβphases at room temperature, except a little ofαphases. However, some pure Nb particles can be observed in all the samples fabricated by CS. It will cause the composition ofβphase differs from that of nominal composition, thus the superelasicity of the samples would be deteriorated. The inhomogeneous composition distribution can be improved through increasing sintering temperature and prolong the sintering times to a certain extent. However, it will cause porosity and pore size decrease obviously, so that it can not meet the biomedical requirement for the porous implant apparatus.It is found that porous Ti-22Nb-6Zr alloys fabricated prepare of sintering prealloy powder by high energy ball milling show homogenous composition distribution, moreover the composition ofβphase is close to that of the nominal composition. This is due to orignial powders become more and more finer with prolong the ball milling times, and three powder element combined tightly in flake shape, it will enhance the atomic diffusion during sintering. Thus, the porous Ti-22Nb-6Zr alloys with homogeneous composition can be obtained. Furthermore, these porous Ti-22Nb-6Zr alloys fabriaced by the method show high porosity (about 45%), low elastic modulus (2.6GPa), relatively high compressive strength (>200Mpa) and good superelsticity (>2.4%), as well as good cycle stablity. It is also found that these alloys even exhibit better superelasticity than that fricated by CS with lower porosity (about 28%).The porous Ti-Nb based superelastic alloys fabricated by combining ball milling with sintering show relative small pore size. In order to increase the pore size, and maintain the superelasticity of these alloys still meet the requirement of biomedical implantation, the effect of the content of space holder NH4HCO3 on the pore characteristics and superelasticity were investigated in this study. It is found that the porisity and pore size increase very obviously with increasing the NH4HCO3 content, while the superelasicity deteriorated greatly...