Environmental Engineering Reference
In-Depth Information
Figure 6.51
Typical aluminide coating microstructures formed on U-700 by (a) high-
activity process and (b) low-activity process. Magnification 1000
, both parts reduced
to 50% for reproduction [71].
ings are generally tailor-made for a given alloy composition. Significant improve-
ments in the oxidation and hot corrosion resistance of aluminide coatings can be
achieved by predepositing of a noble metal, specifically platinum and/or rhodium.
The noble metal is generally electroplated as a thin (0.40
m) layer before the
aluminizing process. In the low-activity process for nickel-based superalloys, to
avoid the deleterious effect of titanium, which is often present in the alloy, a
suitable predeposit of titanium-free Ni-based alloy is often recommended to trap
Ti in the form of Ti(C,N). Similarly, in a high-activity process, predeposit of a
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