铸态镍钛形状记忆合金压缩变形行为及组织演变

摘要

通过真空自耗电极电弧熔炼法制备等原子比镍钛形状记忆合金铸锭.应用差示扫描量热分析、X射线衍射分析、能谱分析和显微分析等技术研究铸态镍钛形状记忆合金在不同温度和不同应变速率压缩加载下的组织演变和变形行为.铸态镍钛形状记忆合金的显微组织由树枝晶和等轴晶组成,成分不均匀,存在偏析.在室温下,铸态镍钛形状记忆合金是B19'马氏体、B2奥氏体和Ti2Ni的混合物.铸态镍钛形状记忆合金在高温压缩变形下对应变速率敏感,铸态镍钛形状记忆合金在0.1 s-1和0.01 s-1应变速率下具有动态再结晶的特征,而在0.001 s-1应变速率下则表现出动态回复的特征.在室温和-100℃时,应变速率对铸态镍钛形状记忆合金的显微组织和真实应力应变曲线影响不大.%The as-cast ingot of equiatomic nickel-titanium shape memory alloy (SMA) was prepared via vacuum consumable arc melting.Differential scanning calorimetry (DSC),X-ray diffraction (XRD) analysis,energy dispersive X-ray (EDX) measurement and microanalysis were adopted in order to understand the microstructure evolution and deformation behavior of the as-cast NiTi SMA under compression at various strain rates and temperatures.The microstructures of as-cast NiTi SMA composed of dendritic grains and equiaxed grains are inhomogeneous and show segregation.The as-cast NiTi SMA consists of B19' martensite,B2 austenite and Ti2Ni phase simultaneously at room temperature.The as-cast NiTi SMA is sensitive to strain rate under compression at high temperature,at which NiTi SMA is characterized by dynamic recrystallization at strain rates of 0.1 and 0.01 s-1,but by dynamic recovery at strain rate of 0.001 s-1.The strain rates have little influence on the true stress-strain curves as well as microstructure of NiTi SMA at room temperature and -100 ℃.