Elevated Temperature Stability of a Co-Cr-C In-Situ Composite.
DREXEL UNIV PHILADELPHIA PA DEPT OF MATERIALS ENGINEERING
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Monovariant eutectic alloys of Co-Cr-C offer potential in advanced gasturbine technology. Key to performance is stability of microstructure and hence strength integrity at elevated temperatures. To assess microstructural stability, composites of composition Co-41 Cr-2.4 C were subjected to isothermal exposures at homologous temperatures of 0.85, 0.89, and 0.92 respectively, for times up to 2500000 S. The composite consists of an aligned rod-like reinforcement of Cr,Co7C3 at Vf 0.3 in a colbalt-rich solid solution matrix. Transverse sections were examined as a function of T,t by a combination of optical and scanning electron microscopy and provided the basis for a detailed and quantitative evaluation of changes in rod density number per unit area, rod spacing, spread of spacings, rod shape and shape spread. While the observations confirm good high-temperature stability, changes in microstructure occured with an associated decrease in rod density. The faceted appearance of the carbide rods, characteristic of the as-grown condition, gave way to a more rounded appearance. Subtle manifestations of structural instability exist which are related to the irregular cross-sectional form of the rod carbides in the as-grown composite. Data have been analyzed in terms of the competing coarsening mechanisms of two-dimensional ripening, fault migration and fault migration plus annihilation. Author
- Laminates and Composite Materials
- Properties of Metals and Alloys
- Jet and Gas Turbine Engines