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متالوژی::
پوشش آلومینیدی
Unacceptable levels of oxidation of the nickel- and cobalt-based superalloys accompanying high operating temperatures spurred the development of aluminide coatings, many of which are still used.
Aluminide coatings provide a substantial amount of aluminum at the surface of the component, although its resistance to oxidation does not differ considerably from the more resistant alloys.
For instance, the oxidation life of a typical diffusion aluminide coating at 2075F for X-40 is 23 h, while for CMSX-3 it is 85 h, 100 h for Rene 80, and 300 h for Rene 125.
The tem- perature at which incipient melting occurs is another factor, and even though NiAl melts around 2900F and superalloys at about 2300F, some melting does occur at as little as 2050F in the diffusion zone of aluminide coated parts.
Overlay coatings perform in the same manner as diffusion aluminide coats, with the presence of chromium and yttrium enhancing the activity of aluminum to form and resist spalling of Al2O3 scales.
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