IMPROVEMENTS OF SCALE ADHERENCE ON HEAT-RESISTING ALLOYS AND COATINGS BY RARE-EARTH ADDITIONS

[摘要] Addition of rare earth elements to heat-resisting alloys and coatings to prevent the spallation of corrosion-resistant Cr2O3 and Al2O3 scales has been known for some time. However, the exact mechanism by which the rare earths improve scale adherence is still a matter of controversy. In this paper, several of the mechanisms proposed to explain the rare earth effect are discussed. It is concluded that, depending on the alloy composition, the rare earths improve scale adherence by several different mechanisms. These include the elimination of void formation at the alloy-scale interface and decreasing the scale thickness of Cr2O3 scales, and the changes in scale microstructure and morphology for Al2O3 scales. Development of an irregular alloy-scale interface and the gettering of the indigenous alloy impurities by the rare earth additions are also important for the adherence of both types of scales. A uniform distribution of the oxide dispersions in or over the alloy is recognized as an important factor which affects their effectiveness.

[发布日期] 1990-12-05

[效力级别]  Proceedings Paper