This paper reports the successful co-deposition of inclusion-free chromiummodified aluminide coatings using a pack-cementation process. The substrate used was the nickel-base superalloy, René 80H. The coatings were of the outward-diffusion type; however, unlike the usual outward-diffusion coatings, the present coatings were relatively free of pack inclusions. The coatings consisted of α-Cr precipitates in a matrix of β-NiAl. The morphology and distribution of the α-Cr precipitates could be adjusted to the extent that two types of coating structures could be obtained. The Type I coating structure contained lamellar α-Cr precipitates situated in the surface region of the coating, whereas the Type II coating structure contained small, spheroidal α-Cr precipitates distributed throughout the outer of a two-layered coating. Both coating types exhibited significantly improved hot-corrosion resistance in a 0.1% SO2-O2 environment at 900°C compared to a commercial aluminide coalting. A study of the corrosion behavior of Type I coatings containing pack inclusions showed that the inclusions were deleterious to the corrosion resistance of the coatings. The corrosion behavior of chromium-aluminide coatings was dependent on both the distribution and amount of α-Cr precipitates in the coating.
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Gleeson, B., Cheung, W.H., Costa, W.D. et al. The hot-corrosion behavior of novel CO-deposited chromium-modified aluminide coatings. Oxid Met 38, 407–424 (1992). https://doi.org/10.1007/BF00665662
- chromium-modified aluminide coatings
- hot corrosion
- pack inclusions