低氧分压下NiTi记忆合金氧化行为的研究

Study of oxidation behavior of NiTi alloy under low oxygen partial pressure

摘要:

本文研究了NiTi形状记忆合金在H₂-H₂O气氛下400-700 °C的氧化行为。合金的氧化过程遵循立方规律,氧化激活能127.52 kJ/mol。氧化显著降低了试样表面的Ni含量。400 °C氧化的试样,其表面形貌与其他试样不同,并且氧化膜较薄,截面结构无法用SEM分析。500 °C、600 °C、700 °C氧化的试样,表面有两种形貌的氧化物,一种是颗粒状氧化物,另一种是晶须状氧化物。截面分析表明,氧化膜分为两层,上层由TiO₂构成,下层由Ni₃Ti构成,两层界面处有孔洞生成。

Abstract:

The isothermal oxidation behavior of NiTi alloy in H₂-H₂O at the temperature range of 400 °C to 700 °C was studied. The oxidation rate followed cubic laws, and the activation energy for the oxidation of the alloy was determined to be 127.52 kJ/mol. The surface Ni content was significantly reduced by selective oxidation. For the sample oxidized at 400 °C, the morphology was different from that formed at high temperatures. For the samples oxidized at 500 °C, 600 °C,and 700 °C, the oxide scales showed two morphologies, which consisted of cubic grains and oxide whiskers. Cross-section analysis showed that the oxide scales consisted of an outer TiO₂ layer and an inner Ni₃Ti layer. Voids formed near the interface of the two layers.