溶胶-凝胶法涂覆氧化铈对铬表面氧化膜生长机制的影响

Effect of Ceria Sol-Gel Coating on the Growing Mechanism of Oxide Film Formed on Chromium

采用溶胶-凝胶法在纯铬表面涂覆纳米氧化铈,并对其在1000℃空气中的氧化行为进行了研究,对于了解稀土元素改善合金抗氧化机理及开发新型稀土掺杂陶瓷防护涂层具有重要意义.采用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对铬表面氧化膜的微观形貌与结构进行观测,用激光拉曼(Raman)和X射线衍射(XRD)对铬及其涂覆纳米氧化铈样品表面氧化膜的应力水平进行测试;并用二次离子质谱(SIMS)对氧化膜内元素Cr、O及Ce的深度分布情况进行了测试.结果表明,纳米氧化铈涂层降低了铬的氧化速率,其抛物线速率常数由涂覆前的2.6×10-6mg2/(cm4·s)下降为涂覆后的7.4×10-7mg2/(cm4·s),并且显著细化了表面Cr2O3膜的晶粒尺寸.这种细晶氧化膜可以通过高温蠕变的方式释放掉部分膜内压应力,并呈现出褶皱特征.纳米氧化铈的存在使Cr2O3膜的生长机制由原来的Cr3+向外扩散控制转变为O2-向内扩散控制.X射线衍射和激光拉曼测量均反映出表面涂覆氧化铈所引起的Cr2O3膜内应力降低;此外,结合氧化膜生长机制的转变对两种应力测量结果之间的偏差进行了分析.

Oxidation behavior of chromium with superficial ceria sol-gel coating was studied at 1 000 ℃ in air with the purpose of clarifying the related mechanism and possible application of new type of rare earth-doped ceramic protective coatings. Scanning electron microscopy（SEM） and transmission electron microscopy（TEM）were used to examine the morphology and microstructure of oxide films formed on chromium. Laser Raman spectrometer and X-ray diffraction （XRD） spectrometer were also used to study the stress status in oxide films formed on Cr with and without CeO2 coating. In addition, depth distribution of element Cr, O and Ce in oxide film was examined by secondary ion massive spectrum （ SIMS ）. Results show that nano-CeO2 coating reduces the growing speed and grain size of Cr2O3 film. The parabolic oxidizing parameters for pure Cr and CeO2-coated Cr were 2.6×10^-6 mg^2/（cm^4, s）and 7.4×10^-7 mg^2/ （cm^4·s）, respectively. This fine grain-sized Cr2O3 film relieved part of the internal compressive stress by means of high temperature creeping and maintained ridge character. The nano-CeO2 coating changed the film growing mechanism from predominant Cr^3＋ cation outward diffusion to O^2- anion inward diffusion. XRD and Raman stress testing results indicate the stress decli nation effect due to nano-CeO2 application;meanwhile, the discrepancy between the two testing results was analyzed in detail concerning to the growing mechanism change of Cr2O3 film formed on chromium.