Influence of alloy additions on oxidation

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Abstract
Some of the important principles of alloy oxidation are discussed, with emphasis on the formation of protective Cr2O3, Al2O3, and SiO2 scales on iron and nickel base alloys. The competition between internal and external oxidation is considered and it is shown how establishment of the protective layer is influenced by various parameters, including alloy interdiffusion coefficient, oxygen solubility and diffusivity in the alloy, and the relative growth rates of the various oxides. The importance of the transient stage of oxidation is emphasised, with particular reference to the population densities of the initial nuclei of the protective oxide and the rates of growth and coalescence of these particles to develop the healing barrier layer. Consideration is given to the effectiveness of the protective scales in service, with respect to transport processes and mechanical integrity. The influence of the minor alloying elements, manganese, titanium, aluminium, silicon, molybdenum, and niobium, on oxidation of Cr2O3 forming alloys is discussed. MST/1017