采用恒温氧化法, 结合Ｘ射线衍射(XRD)、扫描电镜(SEM)及能谱分析(EDS)等手段, 研究了Ti44Ni47Nb9形状记忆合金(SMA)的抗高温氧化性能. 结果 表明, Ti44Ni47Nb9合金在450 ℃下轻微氧化; 600-800 ℃高温下 氧化增重曲线符合抛物线规律, 氧化膜外层主要是金红石型TiO2, 中间为富 Nb层, 内层为富Ni的Ni3Ti层. 研究表明, Ti44Ni47Nb9合金 中的Nb元素减少了TiO2中的氧空位, 形成的富Nb阻挡层, 能有效地抑制Ti元素 的外扩散, 同时也阻挡了氧的内扩散, 降低了氧的固溶度, 从而抑制了 Ni3Ti层中Ni元素的进一步氧化, 提高了合金的抗高温氧化性能.
The isothermal oxidation resistance of Ti44Ni47Nb9 shape memory alloy (SMA) in air over the temperature range of 450-850 ℃ was studied by using XRD, SEM and EDS techniques. Light oxidation was found on the alloy surface at 450 ℃. The alloy was attacked by oxidation and the oxidation kinetic curves were approximately parabola within the temperature range of 600—800 ℃. Experimental results indicate that a multi-layered scale was formed, consisting of an outer rutile layer, a Nb rich intermediate layer and a thin inner Ni3Ti layer. It was found that the Nb rich intermediate layer was compact, which obviously improved the oxidation resistance of the alloy due to its effective inhibition to diffusion of oxygen and titanium. Furthermore, the internal oxidation of nickel element was also inhibited because of the existence of Nb rich layer, which reduced oxygen concentration in the alloy.
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