Discharge Ti-35Nb-7Zr-5Ta Alloy Plasma Sintering And Microstructure And Mechanical Properties

Titanium and titanium alloys have good mechanical properties, excellent corrosion resistance and biocompatibility, and has become the first choice of biomedical implant materials. In recent years, the β biomedical titanium alloys, which have better properties, have now received considerable attention and investigated heavily. Among these β biomedical titanium alloys, the Ti-35Nb-7Zr-5Ta alloy has proved to be a typical representative. At present, the preparation of Ti-35Nb-7Zr-5Ta alloy generally adopts the vacuum smelting method. But the Nb,Ta elements’ melting points and densities are very high, which leads to the poor plastic and unworkability. Then this causes the more complicated preparation process and higher cost.Spark Plasma Sintering(SPS) is a new type of special powder sintering technology. This technology has the benefit of lower sintering temperature, faster heating and cooling rate, shorter sintering time, higher density, the cleaner preparation process and so on. The microstructure of the Ti-35Nb-7Zr-5Ta alloys by SPS is more uniform and fine, and the density is higher. That is beneficial to improve the properties of the alloys,Ti-35Nb-7Zr-5Ta alloys were fabricated by SPS technology in this paper. It mainly discuss the effects of the sintering temperatures and powder sizes on the relative density, microstructure, mechanical properties(the compressive strength and compressive elastic modulus) and fracture morphology. And this paper also researches the effects of the Nb、Ta、Zr elements on the microstructure and compressive elastic modulus.We drew the following conclusions:With the increasing of the sintering temperature, the relative density of the Ti-35Nb-7Zr-5Ta alloy is increasing. At the same sintering temperature, the relative density of the alloy(fine powder) is higher than the alloy(crude powder). Therefore increasing the sintering temperature and decreasing the power size contribute to the increasing of the relative density which is closer to the theoretical density of the alloy. The Ti-35Nb-7Zr-5Ta alloys are mainly composed of β-Ti phase, and a small amount of a-Ti phase. With the increasing of the sintering temperature, the a-Ti phase transform to P-Ti phase gradually. At the same sintering temperature, the content of the β-Ti phase of the alloy(fine powder) is more than the alloy(crude powder), and the content of the a-Ti phase of the former is less than the latter. Therefore increasing the sintering temperature and decrease the power size contribute to get more P-Ti phase.The results show that the microstructure of the alloys are mainly composed of β-Ti phase and the Ti-Nb-Ta-Zr solution phase, and some unmelted Nb, Ta metal particles, and there is a small amount of needle-like a-Ti phase. With the increasing of the sintering temperature, the size of the mixed matrix increases,and unmelted Nb, Ta metal particles melted partially into the sintered base, and the size of the metal particles reduces. At the same sintering temperature, the the size of the mixed matrix of the alloy(fine powder)is bigger than the alloy(crude powder), and the powder size of unmelted Nb, Ta metal particles of the former is smaller than the latter. Therefore increasing the sintering temperature and decreasing the power size contribute to the more fine and uniform microstructure, which is benefit to improve the properties of the alloys.The Ti-35Nb-7Zr-5Ta alloys possess the high compressive strength. With the increasing of the sintering temperature, the compressive strength of the alloys increases. At the same sintering temperature, the compressive strength of the alloys(fine powder) is lower than the alloy(crude powder). This shows that the decrease of the powder size contribute to improve the ductility of the alloy. The research of the fracture morphology of the alloys shows that the fracture mode is brittle fracture,and the fracture surface is cleavage fracture surface. There are some dimples and some micro-cracks in the fracture surface. With the decreasing of the power size contributes to reduce the number and the size of the micro-cracks.The compressive elastic modulus of Ti-35Nb-7Zr-5Ta alloys by SPS is close to the modulus of the alloys which are produced by melting. So the alloys show good mechanical compatibility. With the increasing of the sintering temperature, the compressive elastic modulus of alloys has not changed. At the same sintering temperature, the compressive elastic modulus of the alloys(fine powder)is lower than the alloys (crude powder). This shows that the decreasing of the powder size contribute to reduce the compressive elastic modulus of alloys.These elements of Nb, Ta, Zr which are added to the alloys contribute to the formation of β-Ti phase, which contributes to reduce the compressive elastic modulus of alloys.