Development of strain tolerant aluminia scasles on MCr-AL-Basis high temperatur alloys and coatings

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Recently available results indicate that spallation resistance of the protective alumina scales on MCrAl-type (M=Fe, Ni/CO) alloys and coatings crucially depends on the scale microstructure because scales containing microstrutural defects, such as nano-sized pores and cracks often exhibit a higher fracture toughess, than virtally defect-free, uniform alumina films. The oxide microstructure can, to a large extent be controlled by modifying the minor alloy (coating) composition and by using suitable suface pre-treatments. In the proposed project the effect of the latter parameters on the oxide grain size and porosity formation in the alumina scales will be quantitatively assessed. A quantitative correlation between the oxide microstructure, isothermal oxidation kinetics and fracture toughness of the formed scales will be derived. The scale properties will be characterised by a range of analytical techniques with emphasis on quantitative SEM studies and piesospectroscopic stress measurements. The knowledge derived in these studies can be used as a guideline for development of MCrAl-type alloys (coatings) with extended service lives.