Tribocorrosão de metais duros em meios ácidos

• Ano de defesa: 2025
• Autor(a) principal: Oliveira, Daniela Nunes
• Orientador(a): Scandian, Cherlio
• Banca de defesa: Strey, Nathan Fantecelle , Alves, Juliane Ribeiro da Cruz
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; Mestrado em Engenharia Mecânica
• Programa de Pós-Graduação: Programa de Pós-Graduação em Engenharia Mecânica
• Departamento: Centro Tecnológico
• País: BR
• Palavras-chave em Português: Tribocorrosão; WC–Co; H2SO4; Dissolução de cobalto; Hematita; Tribocorrosion; Cobalt dissolution; Hematite
• Área do conhecimento CNPq: Engenharia Mecânica
• Link de acesso: http://repositorio.ufes.br/handle/10/20535

Hardmetals are composite materials widely used in industrial applications that demand high wear resistance. Among them, WC–Co, composed of tungsten carbide particles embedded in a cobalt matrix, is the most common, being employed in cutting tools and components for the mining and oil industries. Despite their high wear resistance, their service performance can be compromised in corrosive environments, where the interaction between wear and corrosion accelerates degradation, making the study of tribocorrosion essential. Accordingly, this work investigated the tribocorrosion behavior of WC–Co composites with different cobalt contents (9%, 10%, and 16%) and carbide grain sizes (1.2 µm, 1.3 µm, and 2.5 µm) in acidic media, aiming to understand the interaction between sliding wear and corrosion and their effects on material integrity. The composites were characterized by chemical analysis, X-ray diffraction, grain size measurement, hardness, and density. Sliding wear, corrosion, and tribocorrosion tests were performed, with the latter two conducted in H2SO4 solutions at 0.01 N and 1 N. Synthetic hematite spheres were employed as counterbodies, chosen to simulate typical practical conditions, particularly in iron ore beneficiation. Analyses included friction coefficient determination, triboscopy, electrochemical parameters, mass loss, and surface characterization by optical microscopy, SEM, and EDS. In the sliding wear tests, the friction coefficient exhibited stable behavior (0.21–0.33), and wear rates were on the order of 10−4 mm3/m for the samples and 10−6–10−5 mm3/m for the spheres, without significant mechanical damage, such as grain fracture or pullout. In the corrosion tests, selective dissolution of the binder occurred in 0.01 N, with average mass loss around 0.07 mg/min for all samples. In 1 N solution, 09Co12 and 10Co13 showed average mass losses of 0.08 mg/min, whereas 16Co25 exhibited a significantly higher value of 0.17 mg/min, indicating lower corrosion resistance for the sample with the highest cobalt content. During tribocorrosion, the friction coefficient varied with polarization, and the sample with the highest cobalt content again exhibited the highest wear rates (10−2 mm3/m). SEM images revealed selective binder dissolution and the formation of a pseudopassive tungsten oxide layer, with a shallower dissolution depth than in isolated corrosion, suggesting partial sealing by redistributed corrosion products