Abstract：β-titanium-based shape memory alloy has broad application prospects in the field of hard tissue material, due to their low elastic modulus, and excellent biocompatibility. However, compared to the traditional NiTi shape memory alloy, Ti-based SMA exhibit low critical stress for the stress-induced martensitic transformation, low super elastic recovery rate and poor super elastic stability, which limit their application in practice. It is well documented that grain refinement is an effective way to improve the mechanical properties of beta Ti-based shape memory alloys. Therefore, in the present thesis, a β-Ti-based shape memory alloy, Ti-7.5Nb-4Mo-2Sn was taken as the research object. The alloy was firstly heavily deformed by using Accumulative Roll-Bonding(ARB) method, and then annealed to produce recrystallization to refine the grain size of alloy. The effects of ARB and subsequent annealing treatment in microstructure and mechanical properties were investigated. In this paper, The Ti-7.5Nb-4Mo-2Sn alloy was prepared by using vacuum are melting method prepared, and the as-cast alloy was rolled at room temperature by Accumulative Roll-Bonding(ARB) process, and then rapid annealed at 973K for 5min. The microstructure evolution of the alloy after the ARB process and annealing was investigated by OM and XRD, and the mechanical property and the superelasticity of the alloy were evaluated. It is found that ultra fine grained(1μm) β phase can be obtained in the alloy after 8th ARB process and annealed at 973K meanwhile for 5min. The alloy exhibits the improved superelasticity and stability due to the ultra fine grain with the recovery strain of 5.9 and the recovery rate of 98% when the pre-strain of 6%.
2020, Vol. 41 
