Hot corrosion behavior of low pressure plasma sprayed NiCoCrAlY+Ta coatings on nickel base superalloys

Abstract

Articles you may be interested inMolecular dynamics investigation of interfacial mixing behavior in transition metals (Fe, Co, Ni)-Al multilayer system J. Appl. Phys. 105, 034902 (2009); 10.1063/1.3073899 Thermal stability of the interfaces between Co-, Ni-, and Fe-based ferromagnets in contact with selected nitrides M N ( M = Al , B, Nb, Ta, Ti, and V) Summary Abstract: Effects of superalloy and coating structures on hot corrosion J. Vac. Sci. Technol. A 4, 2905 (1986); 10.1116/1.573657Plasma sprayed WC-Co coatings: Influence of spray conditions (atmospheric and low pressure plasma spraying) on the crystal structure, porosity, and hardness J.The hot corrosion behavior of NiCoCrAIY + Ta coatings obtained by low-pressure plasma spraying has been investigated (type I hot corrosion with T = 850 DC). These coatings have been deposited on two nickel-base superalloys and on a cast alloy of the same composition as the coating. Comparison of the cyclic oxidation behavior at 850 DC between the sprayed coating and the cast alloy shows that the sprayed material exhibits a satisfactory and higher resistance than the cast alloy. In the latter case, repeated spalling of the oxide scale results from fractures often associated with Y -rich oxide protrusions. Hot corrosion experiments (salt-spraying test with T = 850 DC and thermal cycling in air every hour) have been conducted on two cast alloys, NiCoCrAI + Ta and NiCoCrAIY + Ta. The Y -containing alloy has a better corrosion resistance than the other alloy which is subject to extensive oxide spallation. In both cases, morphologies typical of basic fluxing processes, involving Cr, AI, Y, and Ta can be observed in highly attacked zones. Finally, tests on plasma sprayed coatings show a high resistance to hot corrosion of these coatings, regardless of the substrate used: a fine adherent alumina layer is formed, and only a limited fluxing of Cr, AI, and Y takes place. The quite different results obtained on cast and sprayed alloys imply that data relative to cast alloys can be unreliable when one wants to predict high temperature behavior and especially lifetimes of overlay coatings.

Mechanical and microstructural characterisations of NiCrCoAlYTa coatings on superalloys deposited by detonation gun technique

“…5) that as sprayed coatings show c-Ni (solid solution fcc structure) or c9-Ni 3 Al as a principal phase and b-NiAl inter metallic as a minor phase. Similar phases have also been reported by Raffaitin et al, 57 Juarez et al 58 and Frances et al 59 for Praxair Tribomet, chemical vapour deposition and plasma sprayed NiCoCrAlYTa coatings respectively. FE-SEM micrographs with the EDS spectrum corresponding to the morphology of the polished surface of the NiCoCrAlYTa coating are shown in Fig.…”

Surface Engineering for High Temperature Corrosion Resistance

“…If the aluminium content is not too high, Ni-and Co-base alloys consist basically of a ductile y-solid solution containing a dispersion of ~-NiAl or ~-CoAl phases. The actual microstructure can be more complex [33] and include y'-Ni3Al, sigma, M'5Y and Y 2 0 3 phases, in addition to y and ~ in NiCoCrAlYTa alloys. Moreover it has to be borne in mind that the microstructure of MCrAlY alloys may depend on their thermal history (heat treatments and cooling rates).…”