IMPROVEMENT IN THE OXIDATION BEHAVIOR OF AUSTENITIC STAINLESS-STEELS BY SUPERFICIALLY APPLIED, CERIUM OXIDE COATINGS

The influence of superficially applied CeO2 coatings on the isothermal-oxidation behavior, preceded by nonisothermal heating, as well as cyclic-oxidation behavior of three grades of austenitic stainless steel (AISI-316, -321, and -304), in dry air is reported. The superficial coating had a thickness of 2.1 mum. The linear heating rate employed was 6 K min-1 up to a maximum temperature of 1423 K, and the isothermal holding temperature was 1273 K. The results clearly depict that CeO2 coatings not only reduced the rates of scale growth for all three varieties of steel but also imparted improved scale adhesion to the respective alloy substrates, as evident from the fact that the coated steels could withstand a number of thermal cycles without scale rupture. In the bare condition, 321-grade steel exhibited the best performance. However, in the presence of the coating, the improved performances of 316 and 321 grades were almost identical, whereas the 304 variety showed improvement only in the first cycle of exposure. The kinetics results have been substantiated by postoxidation analyses of the alloy/scale combinations by SEM, EDS, EPMA, and XRD techniques to reveal the role of rare-earth-oxide coatings on the observed behavior.