Jerzy Jedliński oral presentation (OA3-Tue2-3-4)
An Application of SIMS to Understanding the High Temperature Corrosion: A Brief Survey
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Physical Chemistry and Modeling of Processes and Surface Engineering and Analysis Lab, Al. Mickiewicza, 30-059 Kraków, Poland
Understanding of the high temperature corrosion and corrosion-induced degradation mechanisms, necessary in order to design materials exhibiting improved performance, requires appropriate insight into a number of processes which occur during service exposures in fairly complex system consisting of the substrate and the reaction product. In currently applied materials the reaction product is a solid layer, the so-called scale, formed on a substrate. The superior scales, the protective ones, are compact, continuous and slowly growing. However, the scale-substrate system is dynamic and degrades during the corrosion exposures the rate of the degradation being dependent on many factors and processes, as the growth mechanism, transport properties and microstructure of the scale, mechanical properties of the scale and of the substrate and interfacial strength as well as the segregation of beneficial and detrimental elements to grain boundaries and/or scale-substrate interface. Elucidation of the corrosion and degradation mechanisms requires studying of these processes and taking into account that: (i) system evolves during corrosion exposures; (ii) evolving scales are frequently non-uniform in terms of their microstructure and morphology, the size of features of interest being of the size of microns or even less. Therefore, appropriate experimental approach has been developed to tackle this issue, which involves Secondary Ion Mass Spectrometry (SIMS) as an important analytical tool.
This paper reviews and critically discusses the application of SIMS to understand the high-temperature corrosion and corrosion-induced processes. Particular attention is paid to: (i) transport processes in the scales approached through a combination of two-stage-oxidation using the 18O2-isotope as a tracer and SIMS; (ii) mechanical failure of the scale involving its cracking and/or spallation from the underlying substrate; (iii) distribution of elements in growing scales and at the scale-substrate interface; (iv) determination of the scale evolution stages. Emphasis is placed to possible misleading interpretation of results of experiments which do not provide sufficient spatial resolution or which average the obtained information over different stages of system evolution and/or material’s degradation. The group of currently best metallic materials for high temperature applications in aggressive gaseous environments, the alumina formers, is used as the source of experimental references.
In summary, the achievements owed to application of SIMS are collected and current challenges pertinent to further application of this method are indicated.