Abstract
The influences of sulfur impurities and Pt incorporation on the scale adhesion behavior of aluminide coatings were studied and compared. Low-sulfur NiAl coatings were prepared on a desulfurized, yttrium-free, single-crystal Ni-based superalloy by a modified version of a conventional aluminizing procedure based on chemical vapor deposition. The sulfur level in the resulting NiAl coatings was measured to be less than ∼0.5 ppmw by glow-discharge mass spectroscopy. Platinum-modified aluminide coatings were synthesized by first electroplating a thin layer of Pt (∼7 μm) on the superalloy, followed by the same low-sulfur aluminizing procedure. The measured sulfur content in the (Ni, Pt)Al coating was substantially higher than that of the low-sulfur NiAl coating due to contamination during the Pt electroplating process. A very adherent α-Al2O3 scale formed on the grain surfaces of the low-sulfur NiAl coating during cyclic oxidation testing at 1150 °C, but scale spallation eventually occurred over many of the NiAl grain boundaries. In contrast, despite the higher level of sulfur in the (Ni Pt)Al coating, a very adherent scale was formed over both the coating grain surfaces and grain boundaries during thermal cycling. These results suggest that Pt additions can mitigate the detrimental influence of sulfur on scale adhesion.
Original language | English |
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Pages (from-to) | 2679-2687 |
Number of pages | 9 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 30 |
Issue number | 10 |
DOIs | |
State | Published - 1999 |
Funding
the result of contamination during the Pt electroplating process. This conclusion is supported by the GDMS data from the electroplated Pt coating (Figure 6(b)).
Funders | Funder number |
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Advanced Gas Turbine Systems Program | |
Department of Energy Office of Industrial Technologies | DE-AC05-96OR22464 |
Lockheed Martin Energy Research Corporation |