Microstructural analysis of flame-sprayed and PTA-deposited nickel-based self-fluxing alloy coatings

In this paper, the results of microstructural analyses, including optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analysis, of the Ni-based self-fluxing alloys NiCrBSi, NiCrBSi–WC, and NiBSi–WC deposited on a previously quenched and tempered (QT) steel substrate 42CrMo4 by flame spraying with simultaneous fusing and plasma transferred arc (PTA) process are presented. The aforementioned microstructural analysis was carried out to determine the microstructural characteristics of the investigated coatings, especially at the coating/substrate interface, and the influences of the spraying and welding technology on the steel substrate. The analysis revealed a change in the microstructure of the coating/substrate interface. Specifically, the diffusion characteristics of certain chemical elements (carbon and iron) from the coating to the substrate and from the substrate to the coating were observed. Additionally, the analysis established the existence of new phases within the coating that arose as a result of the aforementioned diffusion and reaction with chemical elements from the coating. The diffusion of chemical elements was most pronounced in the area of the coating/substrate interface, while it decreased away from this area.