Experimental study. Effects of Thermal Spray Procedure and Thermal Fatigue on Microstructure and Properties of NiCrAlMoFe Coating

This study deals with the behaviour of a nickel based alloy, NiCrMoAlFe, which was thermally sprayed, using flame, plasma, high velocity oxyfuel (HVOF), and high frequency pulse detonation (HFPD) methods, onto a stainless steel substrate. This alloy is used as a coating for heat transfer and structural elements in high temperature regions of boilers, such as superheater and reheater tubes. The microstructure, porosity, oxide content, and microhardness of the various coatings were determined. Thermal fatigue tests, under an atmosphere similar to that of power plant service conditions, were conducted in an experimental combustion chamber and, finally, the adhesion between the substrate and the coating layer was evaluated by means of tensile tests. The results obtained are discussed, with special attention being paid to the specific characteristics of the various spraying procedures.