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On the application of SIMS to study the oxidation mechanisms of alumina formers

Abstract Secondary ion mass spectrometry (SIMS) is widely used to investigate the oxidation mechanism of alumina formers, being various MeCrAl (Me=Fe, Ni, Co) alloys and β-NiAl intermetallic compound. Frequently, it is combined with dedicated oxidation exposures, mostly in atmospheres containing different amounts of oxygen tracer (18O2) in order to investigate the scale growth mechanism. However, there are several practical aspects which have to be taken into account during planning the oxidation experiments as well as during interpretation of their results in order to avoid misleading conclusions. In particular, the effects related to the formation of non-uniform scales as well as to the relationship between the exposure conditions and the scale microstructure and morphology at various stages of its growth should be dealt with. This paper discusses the implications of sputtering process with respect to elemental in-depth distribution profiling and the results of the oxidation mechanism investigation of various alumina formers by means of SIMS. It is shown that the obtained shapes of the SIMS profiles and images strongly depend on the choice of the exposure conditions and on the analysis parameters, including the spatial resolution. The exposure conditions are related to the scale microstructure and morphology, the evolution of which occurs during the oxidation process. Formation of duplex alumina scale is reported which comprises an inner more compact sub-layer and an outer ridged and less-compact sub-layer.