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The purpose of this paper is to synthesize polypyrrole/SiO₂ composite coating on 316 stainless steel (316SS) by cyclic voltammogram and preliminary do research about the valuable effects of SiO₂ particle incorporation within the polymer matrix.

This study is based on elaboration of coating by electrochemical process and of SiO₂ by a sol-gel process.

Electrochemical impedance studies revealed that compared with polypyrrole (PPy), PPy-SiO₂ coating acts as a more protective layer on 316SS against corrosion in 3.5 per cent NaCl. Scanning electron microscopy studies revealed that the PPy-SiO₂-coated 316SS showed more uniform and compact morphology.

To fully disperse SiO₂, a sol-gel method is used. Hydroxyl group is generated on the surface of inorganic particle by the sol-gel method, which improves the inorganic particle dispersion.

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.

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.

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.

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