ARB过程中β钛基SMA显微结构演化及对其超弹性能的影响

本文采用复合轧制（Accumulative Roll-Bonding，ARB）工艺对β钛基形状记忆合金(SMA)进行轧制，然后700℃下快速热处理（保温5min）。利用光学显微镜（OM）和X射线衍射仪（XRD）对合金轧制热处理前后合金相组成与显微组织进行分析，并用电子万能试验机对轧制试样的力学性能和超弹性能进行测试。研究了β钛基形状记忆合金复合轧制过程中显微结构演化规律及对其超弹性能的影响。结果表明：复合轧制工艺能有效细化合金晶粒，经过轧制8道次、700℃/5min快速热处理可得到全β相合金组织，其晶粒尺寸1μm；复合轧制处理后合金的超弹性能得到了改善，在预变形为6%时，其回复变形为5.94%，回复率为99%，表现出稳定的超弹性。

Microstructure Evolution of β-Ti-based SMA in ARB Process and Its Effect on Its Superelasticity

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%.