The Carbide Precipitation Control And Sintering Behavior Of Powder Metallurgy Processed Ti-Nb-based Alloys For Biomedical Applications

Ti–Nb based alloys are excellent third-generation titanium alloys for biomedical applications owing to their low Young’s modulus,excellent corrosion resistance and superior biocompatibility.Powder metallurgy is a technology of manufacturing metal materials using metal powders as raw materials.It has been applied to the research and development of titanium alloy for more than 40 years.For the Ti-Nb alloy,the addition of niobium(Nb)element to titanium(Ti)reduces the solubility of the impurity element carbon(C)in the Ti matrix,resulting in the formation of titanium carbide(TiCx)precipitates,which seriously reduces the elongation.In addition,the excessively high sintering temperature and long time required for the densification and composition homogenization of the powder metallurgy Ti-Nb alloys lead to coarse grains and precipitates,which is not conducive to improving the mechanical properties of the powder metallurgy Ti-Nb alloys.In order to solve the above problems of Ti-Nb alloys for biomedical applications,this study started from the two aspects of reducing the carbide content and optimizing the sintering process.To control of carbide,this study mainly uses heat treatment and alloy modification.The optimization of the sintering process is mainly to use the instantaneous liquid phase accelerated diffusion in the sintering process to improve the sintering efficiency and reduce the temperature and holding time of the finished component homogenization and densification.In this study,the addition of bismuth(Hf)element to the Ti-Nb alloys to reduced the TiCx precipitates.The XRD test results show that the addition of Hf increases the lattice constant of Ti,thereby increasing the solubility of carbon in the titanium matrix.At the same time,it is also found that the addition of Fe element in the powder metallurgy Ti-Nb alloys to form the transient eutectic liquid phase can effectively improve the sintering efficiency.The sintering temperature for the homogenization of the Ti-Nb alloys can be reduced to a minimum of 1200℃,and the time is reduced to a minimum of one hour.Specimens were characterized by optical microscopy,environmental scanning electron microscopy,X-ray diffraction,combined with a software-calculated(Ti-Fe)-Nb pseudo binary phase diagram to study the sintering behavior of powder metallurgy Ti-16Nb-5Fe ternary alloys emphatically.According to the characterization and phase diagram calculation results,the sintering process of Ti-16Nb-5Fe ternary alloy is divided into five steps: low temperature solid-phase diffusion step,transient liquid-phase formation step,transient liquid-phase sintering step,high temperature solid-phase diffusion step and sintering homogenization step.In order to solve the problem of coarse grain and precipitated in powder metallurgy processed Ti-Nb-based alloys for biomedical applications.