| Non-toxic, good biocompatibility beta phase stable elements Nb,Zr and Mo were added in titanium alloy in this article. Low elastic modulus Ti-12Nb-12Zr-2Mo alloy has been designed by d-electron alloy design theory and component matching method. Ti-12Nb-12Zr-2Mo alloy has been smelted by water jacketed copper crucible induction melting furnace and upper joint has been casted by investment casting. The internal defects of castings prepared by two different foundry programs have been inspected and analyzed with X-ray detection apparatus.The phase composition ,microstructure,tensile properties and modulus of elasticity of Ti-12Nb-12Zr-2Mo alloy have been studied by X-ray diffraction, optical microscopy,scanning electron microscopy,transmission electron microscopy and universal material testing machine. The influence of heat treatment process on microstructure, tensile properties and modulus of elasticity of Ti-12Nb-12Zr-2Mo alloy at room temperature and low temperature have been analyzed emphatically.Detection of defects results of the castings indicate that shrinkage cavity exist in big hot spot and the last solidification of the castings prepared by two different foundry programs, but the second foundry program is better than the first. The size of the shrinkage cavity of sample casting dissected is smaller than 1mm after cutting.The results of X-ray diffraction indicate that microsture of Ti-12Nb-12Zr-2Mo alloy consists ofα+βphases before and after 730℃×1h,780℃×1h annealing treatment. The average grain size of Ti-12Nb-12Zr-2Mo alloy as-cast is between 300-400μm. The morphology ofαphase is acicular who mainly aligns along three directions. The angle of two neighboring directions is between 30 degrees and 60 degrees. Morphology as-cast observed by TEM is lath andαphase refines after 730℃and 780℃annealing. Microsture of Ti-12Nb-12Zr-2Mo alloy after 830℃×1h annealing treatment constitute by martensiteα′+βphases, martensite distribute diffuse .Martensite transformed earlier is thick slip and later is small needle.The average grain size has reached 500μm. With the energy spectrum analyses, it is found that Nb,Mo,Zr enriched inβparent phase and were poor inαphase. Content of atoms in martensite is as same asα′+βphases after annealing at 830℃for 1h. The Vickers hardness of Ti-12Nb-12Zr-2Mo alloy at room temperature increases with the increasing of annealing temperature. The Vickers hardness after annealing at 830℃for 1h is the highest and increases 12.5% than as-cast.The test results show that tensile strength increases and elongation decreases both with percentage reduction of area after annealing at 830℃for 1h at 0℃,-25℃and -50℃. It is no significant change in elastic modulus who retain between 70 and 75GPa. The modulus of elasticity of Ti-12Nb-12Zr-2Mo alloy is smaller 36% than Ti-6Al-4V, and is close to the elastic modulus of nearβtitanium Ti-13Nb-13Zr (aged) developed by the USA. Ti-12Nb-12Zr-2Mo alloy has certain application potentiality for clinical medicine. |
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