Growth mechanism of the interdiffusion zone between platinum modified bond coats and single crystal superalloys

Abstract

Pt-modified β-NiAl bond coats are applied over the superalloys for oxidation protection in jet engine applications. However, as shown in this study, it also enhances the growth of the interdiffusion zone developed between the bond coat and the superalloy along with brittle precipitates. Location of the Kirkendall plane indicates that a precipitate free sublayer grows from the bond coat, whereas another sublayer grows from the superalloy containing very high volume fraction of precipitates. With increasing Pt content, thickness of both the sublayers increases because of an increase in diffusion rates of the components. Quantitative electron probe microanalysis indicates high concentration of refractory components in the precipitates. Transmission electron microscopy shows that René N5 superalloy produces TCP phases μ and P, whereas CMSX-4 superalloy produces μ and σ in the interdiffusion zone. With increasing Pt content in the bond coat, the average size of the precipitates decreases when coupled with René N5. Precipitates become much finer when the same bond coats are coupled with CMSX-4.