Abstract:

The isothermal and cyclic oxidation hehaviors of pure chromium and the chromium coated with CeO₂ were studied at 900 "C in air. The morphology and microstructure of the oxide films were then ohserved hy means of SEM , TEM and high-resolution electronic microscopy (HREM). Moreover , the cracking and spalling of the oxide films were mon山red on line hy using the acoustic emission (AE) technique , and the distrihution of AE signals in
the time and numher 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. ahility of Cr in isothermal and cyclic oxidation conditions; (2) the main reason for the improvement of anti -oxidation ahility 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 hetter high-temperature plasticity and can relieve a part of the internal compressive stress hy means of high-temperature creeping , thus resulting in ohvious ridge character and relatively low internal compressive stress level; and (4) the adhesion of Cr₂O₃ film on Cr suhstrate greatly improves as the size and numher of film/ suhstrate interfacial defects decrease due to the ceria coating.

Key words: oxidation, coating, acoustic emission, stress, ceria, chromium