Refusão a arco elétrico de revestimentos aspergidos termicamente: impacto da trajetória de refusão

Abstract

The application of Fe-Cr-Ni-based coatings is commonly carried out with the aim of enhancing the corrosion performance of components fabricated from carbon steel. Thermal spray processes are widely employed in industry for depositing these coatings due to their low cost and ease of execution. However, the high porosity, oxidation, and resulting low adhesion/cohesion of the coatings have been a limiting factor in certain conditions. In order to address this issue, several studies have been conducted to reduce porosity and enhance the adhesion/cohesion of the coatings through remelting operations. Among the various available techniques for this purpose, the use of electric arc has shown promising results in practical applications, offering improvements in the characteristics and performance of the coatings, along with low cost and high applicability in the manufacturing sector. In this context, the objective of this undergraduate thesis was to evaluate the effect of remelting using the gas-tungsten arc welding process with a tungsten electrode on the characteristics of Fe-Cr-Ni alloy coatings deposited by electric arc thermal spraying onto a carbon steel substrate. The influence of the remelting path was specifically investigated, as an influential parameter. The microstructure of the remelted coatings was analyzed using optical and scanning electron microscopy. The chemical composition and phases present were identified using energy-dispersive spectroscopy and X-ray diffraction techniques, respectively. The evolution of hardness was assessed through Vickers microhardness measurements. The obtained results confirm that the gas-tungsten arc welding process can be successfully applied in the remelting of thermally sprayed coatings, ensuring a complete bond between the coating and the substrate, with minimal dilution between them. The results also demonstrate that, although occasional variations in the thermal cycle resulting from the adopted remelting path may lead to slight local variations in grain size, they are incapable of generating significant differences in dilution between the coating and the substrate, in their microconstituents, and in the mechanical properties of the remelted surface.