Determination of Corrosion Layers and Protective Coatings on Steels and Alloys used in Simulated Service Environment of Modern Power Plants

Abstract

Abstract The development of modern power generation systems with higher thermal efficiency requires the use of constructional materials of higher strength and improved resistance to the aggressive service atmospheres. The following two examples are discussed: 1. The oxidation behaviour of 9 wt.-% Cr steels in simulated combustion gases: The effects of O2 and H2O content on the oxidation behaviour of 9 wt.-% Cr steels in the temperature range 600—800°C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion. In contrast, that in the presence of water vapour, after an incubation period, the scale became non-protective as a result of a change in the oxidation mechanism. Oxidation experiments on 10 wt.-% Cr steel in simulated steam atmosphere at 650°C have shown that a hematite layer is already formed. The investigation suggest that several independent processes such as oxide dissociation and solid state diffusion of iron cations in the scale significantly contribute to the overall oxide growth process. 2. The development of light-weight intermetallics of TiAl-basis: TiAl-based intermetallics are promising materials for future turbine components because of the combination of high temperature strength and low density. These alloys, however, posses poor oxidation resistance at temperatures above 700°C. The experimental results showed, that the oxidation behaviour of TiAl-based intermetallics can be strongly improved by minor additions of 1–2 at.-% silver.