Appraisal Keynote: Future Trends and Developments

Abstract

The paper briefly summarizes important effects of active elements on the oxidation behaviour of metals and alloys -particularly using chromia scales as examples. In the author’s evaluation available results suggest that the effects may generally be interpreted on the basis of the following mechanistic model: i) scale growth mainly takes place through grain boundary diffusion and ii) the active elements exert their effects through enrichment/segregation at grain boundaries and thereby on the diffusional transport through the scales, grain growth, high temperature creep, etc. of the scales.

With regard to future trends and developments the author is convinced that the key to understanding effects of active elements — and also many other aspects of protective oxidation — lies in improved understanding of interfaces and grain boundaries (structures, enrichment/segregation phenomena, transport properties) and the resultant effects on growth and properties of protective scales. Such knowledge can only be obtained through the characterization coupled with carefully controlled corrosion studies. It is proposed that a coordinated, cooperative research programme should be initiated in order to secure faster progress in the field and to obtain necessary basic data for developing high temperature materials.