Metallography of Aluminide Coatings
AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA)
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The Corrosion Control group at ARL has commenced a programme for evaluating protective coatings for gas turbine blades currently used by the RAAF work previously performed at MRL. To enable examination and evaluation of metallographic specimens with particular attention given to surface features, techniques have been developed for sample preparation and microstructural etching. In developing these techniques, Allison T-56 turbine engine blades cast from a nickel-based superalloy IN 738 and coated with nickel aluminide were sectioned. The nickel aluminide coating applied by a high-activity pack-cementation process to the outer surface of the blades, imparts oxidationcorrosion resistance to the substrate superalloy. Metallographic procedures were developed with an aim to minimise edge rounding and highlight the detailed microstructure by selective etching.
- Metallurgy and Metallography