ARB过程中β钛基SMA显微结构演化及对其超弹性能的影响

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

论文采用复合轧制(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5 min).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℃/5 min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.

Theβ-Ti-based shape-memory alloy(SMA)has broad application prospects in the field of hard tissue materials,due to its low elastic modulus and excellent biocompatibility.However,compared with the traditional NiTi shape-memory alloys,the Ti-based SMA exhibits low critical stress for the stress-induced martensitic transformation,low superelastic recovery rate and poor superelastic stability,which limit their application in practice.It has been well documented that grain refinement is an effective way to improve the mechanical properties ofβ-Ti-based SMA.Therefore,in the present study,aβ-Ti-based SMA,Ti-7.5 Nb-4 Mo-2 Sn was taken as the research object.The alloy was firstly heavily deformed using the accumulative roll-bonding(ARB)method,and then annealed for recrystallization and grain refinement.The effects of ARB and the subsequent annealing treatment on microstructure and mechanical properties were investigated.In this paper,the Ti-7.5 Nb-4 Mo-2 Sn alloy was prepared using the melting method in a vacuum,and the as-cast alloy was rolled at room temperature through the ARB process,and then rapidly annealed at 973 K for 5 min.The microstructure evolution of the alloy after the ARB process and annealing was investigated with optical microscopy(OM)and X-ray diffraction(XRD),and the mechanical properties and superelasticity of the alloy were evaluated.It is found that after the 8 th ARB process and annealed at 973 K for 5 min,an ultra-fine-grained(1μm)βphase can be obtained in the alloy.Because of the ultra-fine grains with the recovery strain of 5.9 and the recovery rate of 98%at the pre-strain of 6%,the alloy exhibits improved superelasticity and stability.