The research was carried out in two phases. The first phase involved the assessment of the oxidation resistance of various alumina formers (both selected industrial materials and specially prepared model materials) to determine the limits of alumina-based protection. In particular, the role of the substrate material was investigated in order to fill a gap in the present state of art concerning its effect on the oxidation mechanisms and resistance of alumina forming materials. The results of the latter were combined with the models of adhesion at the metal/oxide interface and of cohesion within the oxide scale to develop models of the failure mechanisms of alumina scales. The second phase relied on the computer-aided development and experimental validation of an integrated multi-parametric model of alumina-based protection and resulted in a unified model of alumina-based protection, together with practical criteria for the design of materials having improved oxidation resistance.
This integrated model finds its immediate application in predicting lifetimes of massive tubings and sheets or other simple geometries with wall thicknesses in the millimeter range or more. Because of the interdependence of the mechanical and chemical properties of the scale/substrate system the model sets up the frame for further fundamental research on the behaviour of complex geometries.
Corrosion is a major cost to all industrial nations.Material wastage consumes up to 5% of the gross national product.At elevated and high temperatures, in aggressive environments, corrosion is not only seen as an economic problem but also as a fundamental process determining the lifetime of structural materials.In practice, degradation of materials occurs through failure of protective oxide scales, i.e.alumina scales growing on most of the currently available materials for high temperature applications.Therefore this research programme is aimed at assessing the limitations of the current materials and improving their oxidation resistance through improving the failure resistance of alumina scales.
The project has two industrial and technical objectives:
1. Modelling of the alumina scale failure and of the alumnia-based protection against oxidation at high and ultra high temperatures.
2. To specify criteria for alumina scales with improved failure resistance and for the further progress in design of alumina-forming materials.
The research will be carried out in two phases.The first phase will involve the determination of the mechanisms of alumina-based protection and its limitations.On this basis the empirical models of the failure mechanisms of alumina scales will be developed.The second phase will rely on the computer-aided development of a finite element method-based multi parametric model of the alumina-based protection and on the model validation.An iterative procedure will be adopted in this phase which will enable successive improvement of the models.A unified model of the alumina-based protection will lead to practical criteria for the design of materials having improved oxidation resistance.Due to modelling of the adhesion at the metal/alumina interface the latter applies also to the increasingly considered for high temperature applications the metal matrix composites in which matrix comprises alumina-forming material which are reinforced by alumina fibers.
Funding SchemeCSC - Cost-sharing contracts
MK43 0AL Cranfield,bedford
L69 3GH Liverpool