RESUMO O presente trabalho teve como objetivo desenvolver e caracterizar revestimentos nanocompósitos de Ni e Ni-Grafeno aplicados em superfície de aço API 5L X80, utilizando o processo de eletrodeposição, para obter melhores propriedades anticorrosivas. Corpos de prova de dimensões de 20x20x3 mm foram submetidos à limpeza e preparação metalográfica, para posterior deposição dos revestimentos. Para o processo de eletrodeposição foi utilizado um banho à base de níquel contendo dodecil sulfato de sódio (SDS) como surfactante. Para obtenção dos revestimentos Ni-Grafeno, foram adicionadas partículas de grafeno (0,2g/L) ao banho eletrolítico. Os eletrodepósitos obtidos foram caracterizados por Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV). A resistência à corrosão dos revestimentos foi avaliada por meio de ensaios de Polarização Linear (PL) e Espectroscopia de Impedância Eletroquímica (EIE). A inserção de grafeno ao revestimento promoveu a formação de depósitos com grãos mais refinados, e com a direção de crescimento de cristais bem definida. Foram observados depósitos com estruturas lamelares sobrepostas, associadas ao grafeno incorporado à matriz de Ni. A deposição de grafeno influenciou na orientação preferencial dos grãos durante o processo de eletrodeposição, sendo o plano (200) idenfiticado como a orientação preferencial para o nanocompósito Ni-Grafeno. O revestimento Ni-Grafeno obteve melhor desempenho anticorrosivo em comparação ao revestimento de Ni puro e ao metal base, apresentando valor de potencial de corrosão (Ecorr) mais elevado, menor valor de densidade de corrente de corrosão (icorr) e módulo de impedância (|Z|) superior.
This work aims to evaluate the influence of welding parameters, current intensity and deposition speed, on the bead geometry, dilution, morphology and properties of a nickel-based alloy coating. For this, single beads of Inconel 625 alloy were deposited on the substrate of ASTM A36 Steel, by PTA-P process. The samples were sandblasted and polished. The samples were chemically etched by a solution of 92 mL HCl, 3 mL HNO 3 and 5 mL H 2 SO 4 for 5 minutes. The geometry of the beads (reinforcement height, bead width, penetration and contact angle) was measured through the digital stereoscope microscope. The microstructures of the cross sections were evaluated by optical microscopy and scanning electron microscopy (SEM), to identify the possible presence of precipitated phases in the ferrite matrix. The chemical composition of these present phases, as well as the diffused iron content from the substrate for the coating, were measured by EDX. The type of the phases precipitated by x-ray diffraction in the top samples of the coating were also evaluated, in 1.5 mm height of reinforcement. For mechanical property analysis, the microhardness of the coatings was measured by Vickers microhardness test to evaluate their relationship with the iron present in the coatings, which diffused from the substrate. The results confirmed the influence of welding parameters on coating dilution-Current is the parameter of greatest response. The morphologies of the coatings were presented as a γ matrix with second phase precipitation composed of Ni, Nb, Cr and Mo. The concentration of these precipitations decreased with increasing dilution. This occurred because of the increased migration of Fe present in the substrate of the coating through the diffusion phenomena, with increasing dilution. The Fe reduced the solubility of Nb and Mo of the γ matrix, causing the decrease of its hardness.
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