Avaliação do processo de aplicação de um revestimento de cromo duro com catalisador isento de fluoretos por eletrodeposição em peças de aço carbono

Abstract

Metallic electrodeposition, particularly in the case of hard chrome, is a widely employed technique with the primary objective of enhancing the corrosion resistance of various materials. Despite the presence of toxic and carcinogenic substances in the hard chrome bath composition, understanding this process is crucial due to its significance, especially at the national level. Within this context, this study aimed to evaluate a hard chrome electrodeposition process with the addition of a fluoride-free catalyst, which is currently the most used for achieving higher current efficiency without substrate attack. For this purpose, the process was conducted on SAE 1045 carbon steel parts, without addition (condition 0) and with three different concentrations of a fluoride-free catalyst (30, 50, and 80 mL/L, representing conditions 1, 2, and 3). Field emission gun scanning electron microscopy with (SEM/FE) and energy dispersive X-ray spectroscopy (EDX) analyses were performed to assess the morphology of the coatings and corrosion products formed after the salt spray test. Overall, the results revealed that parts coated with hard chrome under conditions 1, 2, and 3 exhibited microcracked deposits, while those in condition 0 showed only localized faults. Regarding the EDX analyses, the composition maps highlighted a greater exposure of the base material in the catalyst conditions, possibly due to deeper microcracks. Furthermore, optical microscopy images showed that the microcracks were filled with corrosion products, suggesting that they may have acted as channels for corrosion. In terms of salt spray and wet chamber tests, the addition of the catalyst did not provide significant gains in coating and, consequently, protection, as the parts exhibited lower corrosion resistance. This finding was equally evidenced through the data obtained from polarization curves, which showed that the catalyst did not improve this property. Based on the operational parameters applied in this study, the addition of the fluoride-free catalyst did not yield satisfactory results, indicating lower corrosion resistance of the coating compared to the condition without the catalyst. In this regard, it is essential to conduct more comprehensive investigations not only to validate these findings but also to refine the conditions employed in the implementation of this study. [resumo fornecido pelo autor]