Pt-modified aluminide coating

Pt layers results in a two-phase (fi + PtAU) coating use of still thicker layers of Pt results in a complete layer of PtAl2 over the )6-NiAl. The presence of the Pt layer has also been clearly shown to increase the A1 uptake in the coating, for fixed aluminizing conditions. This is the result of the Pt lowering the activity coefficient of A1 in the coating. The Pt-modified aluminide coatings are observed to have markedly improved resistance to cyclic oxidation and hot corrosion. 

Figure 10.16 Optical micrograph showing the cross-section of a Pt-modified aluminide coating on a nickel-base single-crystal superalloy after oxidation at 1200 °C for 20 h. The original grain structure of the /3-phase is evident and y has begun to nucleate at /6 grain boundaries as a consequence of A1 depletion.

Figure 10.25 Scanning electron micrographs showing cross-sections of (a) an as-processed Pt-modified aluminide bond coat indicating defects in the EB-PVD YSZ TBC (b) the same coating which has been cycled part way to failure showing how these defects propagate and produce cracks in the TBC.

Monceau D, Oquab D, Estoumes C, Boidot M, Selezneff S, Thebault Y, Cadoret Y. Pt-modified Ni aluminides, MCrAlY-base multilayer coatings and TBC systems fabricated by Spark Plasma Sintering for the protection of Ni-base superalloys. Surface Coatings Technology. 2009 204 771-778. 

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