表面涂敷氧化铈对铬900℃氧化机理的影响

Influence of Ceria Superficial Coating on Oxidation Mechanism of Chromium at 900℃

对铬及其表面涂敷氧化铈样品在900℃空气中的恒温氧化和循环氧化行为进行了研究.用扫描电镜(SEM)、透射电镜(TEM)和高分辨电镜(HREM)对氧化膜微观形貌及结构进行了观测;并用声发射技术(AE)对铬表面氧化膜的开裂与剥落进行了实时监测,通过相应的氧化膜破裂模型对采集到的AE信号在时域和数域上的分布进行了分析;此外,还用激光拉曼谱对两种样品表面氧化膜的内应力进行了测试.结果表明:表面涂敷氧化铈显著改善了铬的抗恒温氧化及抗循环氧化性能;表面涂敷CeO2提高铬抗氧化性能的原因主要在于CeO2降低了Cr2O3氧化膜的生长速度和晶粒尺寸,这种细晶Cr2O3氧化膜有更好的高温塑性,可以通过高温蠕变的方式释放掉部分膜内压应力,因而具有明显的褶皱特征和较低的压应力水平;此外,涂敷CeO2减少了氧化膜/基体界面缺陷的数量和大小,从而显著提高了Cr2O3氧化膜在基体铬上的粘附性.

The isothermal and cyclic oxidation behaviors of pure chromium and the chromium coated with CeO2 were studied at 900℃ in air. The morphology and microstructure of the oxide films were then observed by means of SEM, TEM and high-resolution electronic microscopy （HREM）. Moreover, the cracking and spalling of the oxide films were monitored on line by using the acoustic emission （AE） technique, and the distribution of AE signals in the time and number domains were respectively analyzed according to the related oxide cracking model. The internal stresses of the oxide films coated on Cr surfaces with and without ceria were finally measured using a Laser Raman spectrometer. The results show that （1） the ceria coating greatly improves the anti-oxidation ability of Cr in isothermal and cyclic oxidation conditions; （2） the main reason for the improvement of anti-oxidation ability of Cr is that the ceria addition greatly decreases the growing speed and grain size of Cr2O3 films; （3） the fine-grained Cr2O3 film is of better high-temperature plasticity and can relieve a part of the internal compressive stress by means of high-temperature creeping, thus resulting in obvious ridge character and relatively low internal compressive stress level ; and （4） the adhesion of Cr2O3 film on Cr substrate greatly improves as the size and number of film/substrate interracial defects decrease due to the ceria coating.