MCrAlY coatings

Plasma spraying, 21 483 Plasma spray MCrAlY coatings, 13 507 Plasma sputtering, 24 730 Plasma tube, 14 655 Plasmid cloning experiments, passenger sequence in, 12 503-504... 

The presence of Y in the coatings improves the oxidation resistance of AI2O3 scale. Thus, MCrAlY coatings outperform diffusion aluminides significantly in oxidation tasks as shown in Table 12.8. 

When MCrAlY coatings are exposed to vanadate impurities, derived from low-grade petroleum fuels, Kofstad and Seiersten (1987) have foxuid that protective AI2O3 or Cr203 scale development is hindered by the presence of molten vanadates. 

Both aqueous and fused-salt electrol3rtes have been used for plating the platinum group elements. Platinum has been used as a diffusion-barrier layer in aluminiding nickel-base alloys and MCrAlY coatings. Platinum... 

The Haynes 214 honeycomb seals and solid MCrAlY coated seals both survived until the end of the highest temperature test. 

Gupta D K and Duvall D S (1984), A Silicon and Hafnium Modified Plasma Sprayed MCrAlY Coating for Single Crystal SuperaUoys, in Gell M, etai.. Superalloys 1984, Warrendale, PA, TMS, 711-720. 

Brandi W, Toma D, Kruger J, Grabke H J, Matthaus G, The oxidation behaviour of HVOF thermal-sprayed MCrAlY coatings . Surf Coat Technol, 1997, 94-5(1-3), 21-26... 

MCrAlY coatings (where M = Co, Ni or Co/Ni) are widely applied to the first and second stage turbine blades and nozzle guide vanes, where they may be used as corrosion-resistant overlays or as bond coats for use with TBCs. Cr and A1 are present in the MCrAlY composition because they form highly tenacious protective oxide scales, whilst Y promotes the formation of these stable oxides. 

Coatings developed some 30-35 years ago, eommonly known as MCrAlY, have a wide range of eomposition tailored to the type of performanee required and are Ni/Co based as shown in these three eommon types of eoatings ... 

Austenitic Ni-Cr-Al aUoys, and aluminide and MCrAlY (M = Ni, Co, or Fe) coatings, which form AI2O3 surface layers, are used to about 1100 °C. 

Intermetallic bond coat (Pt-aluminide or MCrAlY alloy)... 

Bond coat phase transformation Most of the bond coats, either MCrAlY or (Ni,Pt)Al, used in TBCs are based on the P-NiAl phase. As shown in Fig. 10, the major change in the bond coat microstructure during oxidation is the formation of the y -NisAl phase. This is attributed to aluminium depletion caused by the formation of AI2O3 on the surface and by inward diffusion of aluminium into the superalloy. Since the density of P-NiAl (5.9 g/cm ) is smaller than that of y -Ni3Al (7.5g/cm), there is a volume shrinkage during this transformation [68]. If the decomposition of the P-NiAl takes place locally or at a different time in different places, then the volume reduction will also be localised. This may cause the bond coat surface to distort from its original shape or cavities to form inside the bond coat. 

Coatings based on MCrAlY (M = Fe, Ni, Co) are particularly interesting because they contain the same elements as the superalloys. As they are not required to sustain mechanical load, their composition can be chosen uniquely to optimize their corrosion resistance. For example, by increasing the concentration of active elements such as A1 and Y one improves the adhesion of the oxide scales. 

The TBCs deposited by plasma spraying consist (adjacent to the metallic substrate Inconel, Hastelloy, Ti6Al4V) of a dense MCrAlY (M = Ni, Co) alloy bond coat which is laid down by low-pressure plasma spraying (LPPS), followed by a porous stabilized zirconia top coat in the thickness range of 300 to lOOOgm (Cernuschi et al., 2004), as shown schematically in Figure 7.39. During operation. 

Addition of Si to the MCrAlY bond coat to improve its corrosion and erosion resistances. 

While these results show the favourable influence of Y, there remains evidence to show that Y can be leached from MCrAlY-type coatings and cast allo5rs with the formation of a complex oxy-sulphate SO3 + Y2O3 = Y2O2SO4 (Frances et al. 1988). Furthermore,... 

Thermal evaporation uses the atomic cloud formed by the evaporation of the coating metal in a vacuum environment to coat all the surfaces in the line of sight between the substrate and the target (source). It is often used in producing thin 0.5 pm coatings or a very thick 1-mm layer of heat-resistant materials, such as MCrAlY—a metal, chromium, aluminum, and yttrium alloy. 

Primarily used fy improved wear resistany (many coating sterns including ceramics and cermets), but also used for improved yrrosion resistany (aluminum, zinc, and their alloys) and oxidation resistany (e.g., MCrAlY), thermal barrier protection (partially stabilized ziiconia), electrically conductive coatings (e.g., copper and silver), and dimensional restoraticm Improved cmroraon resistany... 

Thermally sprayed coatings, for example, MCrAlY corrosion protection layers and ceramic-based thermal barriers... 

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