Conventional air plasma spray technique and two powders, NiCrAlY and CoNiCrAlY, were used to produce the M-CrAlY type of coating on the Inconel 713LC substrate. Two phase coatings, consisting of Ni and/or Co solid solution and NiAl intermetallic phase, were produced. A certain amount of imperfectly melted powder particles, voids and aluminium oxide was also present. After air plasma spraying the coatings were annealed at widely ranging temperatures (650, 800, 1000 and 1150• C) for two hours in argon-flow atmosphere. It was found that the temperature significantly affects the microstructure of resulting coatings. The oxide scale was formed by internal oxidation in a coating region primarily at higher temperatures. In this case, aluminium was depleted from the NiAl phase within the coating region and the Ni, Co, Cr solid solutions and the aluminium oxide started to form rapidly. No interaction was observed after the short thermal exposure below the substrate surface. The microstructure of coatings was recorded by scanning electron microscope. Coating thickness, amount of voids and oxide scale were measured by means of image analysis. The concentration of phases was estimated by energy dispersive microanalysis.
The specimens in the present study were prepared by air plasma spraying of NiCrAlY coatings onto the INCONEL 713LC nickel-based superalloy substrate surface. Subsequently an aluminium sheet was cladded onto the coating surface by means of uniaxial cold pressing. After that the specimens were annealed at temperatures of 650, 850 and 1000°C for two hours in argon-flow atmosphere. The remelted NiCrAlY coating specimens were annealed at a temperature of 800°C for fifty hours in ambient atmosphere. A scanning electron microscope was used to record the changes in the modified coating microstructure. Chemical composition was measured by means of energy dispersive microanalysis. Qualitative and quantitative x-ray diffraction analysis was used for the final determination of phases. The microhardness of remelted air-plasma-sprayed NiCrAlY coatings before and after short thermal exposure was also measured.
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