Studies of plasma spray coatings on a Fe‐base superalloy, their structure and high temperature oxidation behaviour

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Abstract
Purpose – Plasma spray coating technologies are capable of depositing a wide range of compositions without significantly heating the substrate. The objective is to characterise plasma sprayed metallic coatings on a Fe-based superalloy. Design/methodology/approach – NiCrAlY, Ni-20Cr, Ni3Al and Stellite-6 metallic coatings were deposited on a Fe-based superalloy (32Ni-21Cr-0.3Al-0.3Ti-1.5Mn-1.0Si-0.1C-Bal Fe) by the shrouded plasma spray process. The coatings were characterised in relation to coating thickness, porosity, microhardness and microstructure. The high temperature oxidation behaviour of the coatings was investigated in brief. The techniques used in the present investigation include metallography, XRD and SEM/EDAX. Findings – All the coatings exhibited a lamellar structure with distinctive boundaries along with the presence of some porosity and oxide inclusions. The microhardness of the coatings was observed to vary with the distance from the coating-substrate interface. The St-6 coating had the maximum microhardness, whereas the lowest hardness was exhibited by the Ni3Al coating. The phases revealed by XRD of the coatings confirmed the formation of solid solutions, whereas EDAX analysis of the as-sprayed coatings confirmed the presence of basic elements of the coating powders. So far as high temperature oxidation behaviour is concerned, all of the coatings followed the parabolic rate law and resulted in the formation of protective oxide scales on the substrate superalloy. Originality/value – The plasma spray process provides the possibility of developing coatings of Ni3Al as well as commercial available NiCrAlY, Ni-20Cr and St-6 powders on Fe-based superalloy Superfer 800H