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In situ X-ray diffraction was used to study the oxide formation on AISI 316L stainless steel (SS) specimens during isothermal oxidation at 900 °C in air. Results were compared with those obtained on AISI 304 SS to determine the role of molybdenum on the oxidation process for the AISI 316L SS specimens. Our results show that molybdenum plays a major protective role during steel oxidation. This element is found in a NiMoO4 phase at the internal oxide–metal interface. The high molybdenum content of the alloy hinders the outward diffusion of iron and leads to a lower growth rate and better scale adherence. The oxide scale is then composed of Cr2O3 with a small amount of Mn1.5Cr1.5O4 at the external interface. The improved scale adherence appears to be due to a keying effect at the scale/alloy interface promoted by molybdenum. [ABSTRACT FROM AUTHOR]

The influence of yttrium oxide coating (processed by the sol–gel method) on the oxidation behaviour of a commercial FeCrAl alloy (Kanthal A1) has been investigated during isothermal exposures in air at 1373 K. The scale growth kinetics of the uncoated alloy obey a parabolic rate law during the whole oxidation test, whereas the kinetic curves of the Y-coated specimen exhibit an initial transient stage for the first few hours, followed by a parabolic regime. The yttrium sol–gel coating deposited on the bare alloy does not provide the beneficial effect usually ascribed to reactive elements. No oxidation rate improvement of the coated alloy is observed, the parabolic rate constant values are strictly identical for both specimens. In situ X-ray diffraction reveals a marked influence of the reactive element on the composition of the oxide scale. The oxide layer formed on the yttrium-coated specimen comprised, in addition to α-alumina which is the main oxide also identified on the bare specimen, the presence of yttrium aluminates (YAlO3, Y3Al5O12) located in the outermost part of the layer. [Copyright &y& Elsevier]