通过拉伸试验和差示扫描量热法(DSC)等手段,研究了高温时效和高温、低温循环对镍钛形状记忆合金超弹性和相变行为的影响.结果表明,TNC1605镍钛合金在500℃时效后具有较高的上/下平台强度,并且具有较低的残余应变,马氏体逆相变终了温度Af约为22℃,具有较好的超弹性能.经过10次200℃高温保温4h和液氮中保温4h的高低温循环处理后,下平台强度、6％拉伸加载和卸载后残余应变、Af和超弹性性能参数保持稳定.

The influences of W addition on microstructures and phase transformation behavior of as-cast TiNi shape memory alloy were investigated by differential scanning calorimeter (DSC),X-ray diffraction (XRD),and scanning electron microscope (SEM).The results showed that the phase composition of TiNiW0.3 and TiNiW0.5(atom fraction) alloy were B2 parent phase and Ti2 (Ni,W)precipitate phase at room temperature;TiNiW3 and TiNiW6 alloy were composed of B2 parent phase,Ti2 (Ni,W) and W-rich solid solution phase(W-s),and the shapes of Ti2 (Ni,W) precipitated phases were irregular granular,strip,and fence,while W-s phases were in non-uniform granular shapes,grew up in clusters and dispersed in matrix uniformly.With the addition of W,the grain size of as-cast ingot was refined,and effects of refined crystalline strengthening and solution strengthening occurred.The strength and hardness of the alloy increased with the increase of W content.After solid solution treatment at 850 ℃ for 15 min,the phase transformation in cooling/heating process was A→M/M→A,and the phase transition temperature range became wide,the temperature reduced,and the reducing rate gradually decreased with the increase of W content.

通过差示扫描量热仪(DSC)、X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)研究了固溶时效对Ti-50.8Ni和Ti-50.8Ni-0.3Cr合金显微组织及相变特性影响.结果表明,固溶后两种合金组织都由原始拉拔纤维组织转变为等轴晶粒,晶粒随固溶温度升高而长大,固溶后母相主要是B2(B19')相,同时发现存在TiNi3粒子.两种合金的马氏体相变峰值温度Mp随着固溶温度升高及时间延长先降低再升高.500℃时效0.5 h时Ti-50.8Ni合金加热/冷却相变类型是A→R→M1→M 2/M→Rr→A,Ti-50.8Ni-0.3％ Cr合金相变类型是A→R→M1→M2/M→Rr1→Rr2→A;时效1 h时,两种合金加热/冷却相变类型是A→R→M/M→Rr→A,时效2 h后两种合金加热/冷却相变类型是A→R→M/M→A.

运用循环伏安和极化曲线法研究了镍钛合金在甲酰胺-氨磺酸体系中的电化学反应机制.对阳极极化曲线和Tafel曲线的研究表明, 镍钛阳极的动力学参数为: a=5.6399, b=0.7229, i0=1.5784×10-8 A*cm-2, nβ=0.08.循环伏安法和XPS研究表明, 在本实验条件下, 镍钛合金在甲酰胺-氨磺酸体系中是以整体的形式, 而不是以钛元素和镍元素分别进行阳极溶解的, 该阳极反应为不可逆过程, 为一步7电子的氧化过程, 该阳极反应为: NiTi - 7e → Ti4+ + Ni3+, Ni3+在酸性溶液中极不稳定, 发生还原过程: Ni3++e → Ni2+.

利用直流磁控溅射法溅射沉积了NiTi形状记忆合金薄膜, 对NiTi形状记忆合金薄膜进行晶化热处理以使其获得形状记忆效应, 研究了550 ℃晶化热处理1 h后Ti-48.2% Ni薄膜的相变温度和力学性能. 研究结果表明, NiTi 薄膜550 ℃晶化热处理1 h后, 升温过程中发生M→A的相变, 而降温过程中则先发生A→R相变, 再发生R→M的相变. 薄膜的断裂强度随测试温度的升高而增大, 残余应变随温度的升高而减小, 当温度大于Af点时, 表现为超弹性.

对经过不同表面处理的钛镍合金丝材的力学性能进行了对比分析. 研究表明: 与酸洗及机械抛光相比, 电解抛光可有效改善钛镍丝材的力学性能, 而经电镀工艺处理后的试样则易发生氢脆现象, 从而显著降低材料的力学性能指标.

本文对NiTi合金的电解抛光机理进行了初步的探索.研究表明:NiTi合金的电解抛光特性曲线与典型的电解抛光特性曲线有显著不同,不存在稳定的电流平台区.当试样在低电位区抛光时,抛光速度为反应产物通过粘滞层的扩散速度所控制;而当试样在高电位区抛光时,则以点蚀机制为主.