The oxidation of a Ni–30Cr alloy at 700 °C in impure argon was studied in order to provide new elements of understanding on chromia scale growth in low oxygen partial pressure atmosphere (10 −5 atm). Oxidation tests were carried out during 30 min to 50 h in a thermogravimetric analysis system using a symmetrical balance with in situ monitoring of the oxygen partial pressure. The oxidation kinetics were determined as parabolic with an estimated stationary parabolic constant value of 10 −15 cm 2 s −1 , after a transient stage of about 3 h. The oxide scale was identified as a pure chromia layer by TEM and XPS characterisations. After 50 h at 700 °C, the scale thickness estimated by TEM cross section observation was about 100 nm. A slightly thicker and more porous oxide scale was observed above the alloy’s grain boundaries. The metal/oxide interface also exhibited a deeper recession towards the substrate above the alloy’s grain boundaries. The orientation of chromia grains was determined by TKD (transmission Kikuchi diffraction). A strong preference was noted for the orientation perpendicular to the surface, along the < 0001 > direction of the corundum structure. Finally, the type of semiconduction was determined for the scales formed after 7 h and 50 h of oxidation. For the shorter oxidation time, the chromia scale exhibited an n -type semiconduction, whereas for the longer exposure, both n -type and insulating semiconduction were identified.

中文翻译：

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Ni-30Cr 合金在 700 °C 不纯氩气中形成的铬鳞片的生长动力学和表征

对 Ni-30Cr 合金在 700 °C 下在不纯氩气中的氧化进行了研究，以便为了解在低氧分压气氛 (10 -5 atm) 中氧化铬鳞片生长提供新的元素。氧化测试在热重分析系统中进行 30 分钟至 50 小时，使用对称天平并在原位监测氧分压。在大约3小时的瞬态阶段之后，氧化动力学被确定为具有10 -15 cm 2 s -1 的估计固定抛物线常数值的抛物线。通过 TEM 和 XPS 表征，氧化皮被确定为纯氧化铬层。在 700°C 下 50 小时后，通过 TEM 横截面观察估计的鳞片厚度约为 100 nm。在合金晶界上方观察到稍厚和更多孔的氧化皮。金属/氧化物界面也表现出向合金晶界上方的基材更深的后退。氧化铬晶粒的取向由TKD（透射菊池衍射）确定。注意到垂直于表面的取向，沿着刚玉结构的 <0001> 方向的强烈偏好。最后，确定氧化 7 小时和 50 小时后形成的鳞片的半导体类型。对于较短的氧化时间，氧化铬鳞片表现出 n 型半导体，而对于较长的暴露时间，识别出 n 型和绝缘半导体。注意到垂直于表面的取向，沿着刚玉结构的 <0001> 方向的强烈偏好。最后，确定氧化 7 小时和 50 小时后形成的鳞片的半导体类型。对于较短的氧化时间，氧化铬鳞片表现出 n 型半导体，而对于较长的暴露时间，识别出 n 型和绝缘半导体。注意到垂直于表面的取向，沿着刚玉结构的 <0001> 方向的强烈偏好。最后，确定氧化 7 小时和 50 小时后形成的鳞片的半导体类型。对于较短的氧化时间，氧化铬鳞片表现出 n 型半导体，而对于较长的暴露时间，识别出 n 型和绝缘半导体。