Alumina Scale Adherence to CoCrAl Alloys and Coatings
There are two essential requirements for alloys or coatings which are designed to withstand degradation by oxidation during high temperature exposure. First, they must form a surface oxide which thickens only at a slow rate, and secondly this oxide layer must remain adherent to the alloy surface under all conditions. A12O3 is generally regarded as the best protective oxide: diffusion through A12O3 is relatively slow in comparison with most other oxides, and since it is also stable, relatively little difficulty exists in selecting a composition which contains sufficient aluminium to provide, by selective oxidation, a protective A12O3 scale under various service environments. Typically, these will contain at least 5% A1 (by mass) and usually substantial amounts of Cr.
KeywordsActive Element Protective Oxide Oxide Dispersion Surface Scale High Temperature Exposure
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