Effect Of Alloying Element On The Microstructure And The Related Properties Of Ti-Nb Alloys

Ti-Nb alloys have the advantages of low elastic modulus, super-elastic and shapememory properties, which exhibit a great application potential as a biological graftmaterial. The existing results show that the microstructure and mechanical properties ofTi-Nb alloys mainly depend on the composition of the alloy. The performance of thealloy can be improved significantly by appropriate alloying. In this thesis, the effects ofthe additions of Zr, Mo and Si alloying element on the microstructure, mechanicalproperties and corrosion resistance of Ti-22Nb alloy were studied and the impactmechanism were discussed. The purpose is to provide the theoretical and experimentalguideline for the experiment of mechanical properties by alloying method. The mainresults are as follows:(1) The results show that the solid solution of Ti-22Nb alloy is mainly composed ofacicular martensite α" and β phase, While, the Ti-Nb-Zr alloy and Ti-Nb-Mo alloys iscomposed of a single β phase, the additions of Zr and Mo elements hinder the formationof α" phase during the quenching process. A small amount of Si element can stabilizethe β phase, when the content of Si element is2-4at.%, the solution-treated Ti-Nb-Sialloy is composed of single β phase. When the content of Si element is about6at.%,some intermetallic compounds can form in the alloy;(2) The results of room temperature tensile test show that the addition of Zrelement can improve the mechanical properties of Ti-22Nb alloy after solutiontreatment of800℃. With the addition of Zr element, the strength and the elongation ofthe Ti-Nb-Zr alloys increases, and the Ti-22Nb-6Zr alloy has a maximum tensilestrength of700MPa with the maximum elongation of46.5%. In the solution-treatedTi-Nb-Mo alloy, Ti-22Nb-2Mo alloy has the greatest tensile strength and elongation, it’s648MPa and33%respectively. During the tensile test Ti-22Nb-4Mo and Ti-22Nb-6Moalloy does not appear work harden, showing the characteristics of rubber metal. Thesolution-treated Ti-22Nb-2Si have stable room temperature super-elasticity, when thepre-deformation is3%, the alloy has the maximum recovery strain rate;(3) The results of electrochemical test show that the additiom of Zr, Mo and Sielement can improve the corrosion resistance of Ti-22Nb alloy in a0.9%NaCl solution. From the test of potentiodynamic polarization curve, one can see that the corrosioncurrent density of Ti-Nb-Zr, Ti-Nb-Mo and Ti-Nb-Si alloys decreases with the additionof three elements, the corrosion resistance of the alloys enhanced. The electrochemicalimpedance spectroscopy test get the same results, surface film of the alloy monolayerexpress the characteristics of single-layer structure. With the addition of the thirdelement, the resistance value of the three alloys also increased, so the corrosionresistance of the alloys enhances.