The oxidation behavior of aluminide-coated γ′/δ directional eutectics

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The relationship between the process variables and the property of oxidation resistance was investigated for aluminide-coated γ′/δ directional eutectics by the control of the surface composition and the coating microstructure. The oxidation behavior of coated and uncoated substrates was found to belong to three main groups, depending on the surface composition of the coated or uncoated substrate prior to oxidation and irrespective of the manner in which the coating was processed. The coatings with surface composition in Group I formed protective external scales of A12O3; those with surface compositions in Group II formed nonprotective external scales of niobium-rich oxides; those substrates with surface compositions in Group III formed nonprotective external scales of NiO. The oxidation behavior within each group is herein explained in terms of the coating microstructure. Coatings that possessed a single-phase surface layer demonstrated better oxidation resistance than those with a two-phase lamellar morphology. © 1980 American society for metals and the metallurgical society of AIME.

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Metallurgical Transactions A