Influence of Nanometric Ceria Coating on Oxidation Behavior of Chromium at 900℃

摘要

Isothermal and cyclic oxidation behaviors of chromium samples with and without nanometric CeO_2 coating were studied at 900℃ in air. Scanning electron microscopy (SEM) , transmission electron microscopy (TEM) , and high-resolution electron microscopy (HREM) were used to examine the morphology and microstructure of the oxide film. It was found that ceria coating greatly improved the oxidation resistance of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission (AE) technique was used in situ to monitor the cracking and spalling of oxide film, and AE signals were analyzed in time-domain and number-domain according to related oxide fracture model. Laser Raman spectrometer was also used to study the stress of oxide film formed on Cr with and without ceria. The improvement in oxidation resistance of chromium is believed mainly due to that ceria greatly reduced the growth speed and grain size of Cr_2O_3. This finegrained Cr_2O_3 oxide film might have better high temperature plasticity and could relieve parts of the compressive stress by means of creeping and maintained ridge character and relatively lower level of internal stress. Meanwhile, ceria application reduced the size and number of interfacial defects, remarkably enhanced the adhesive property of Cr_2O_3 oxide scale formed on Cr substrate.