Doutorado em Engenharia Mecânica

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Navegando Doutorado em Engenharia Mecânica por Assunto "Cerâmicos de engenharia"

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    Sobre o comportamento em abrasão de cerâmicos e metais duros e sua correlação com a dureza e a tenacidade à fratura
    (Universidade Federal do Espírito Santo, 2023-12-19) Magnol, Renan Valter; Scandian, Cherlio; https://orcid.org/0000-0002-4393-719X; http://lattes.cnpq.br/8466752738430250; https://orcid.org/0000000300378663; http://lattes.cnpq.br/8908470772061353; Sinatora, Amilton; https://orcid.org/0000-0002-5004-4947; http://lattes.cnpq.br/2988437176012972; Mello, José Daniel Biasoli de; https://orcid.org/0000-0001-8912-2132; http://lattes.cnpq.br/1696467778255755; Mello, Valdicleide Silva e; https://orcid.org/0000-0001-6413-6650; http://lattes.cnpq.br/4147387781308845; Strey, Nathan Fantecelle; https://orcid.org/0000-0002-2568-116X; http://lattes.cnpq.br/3613706957012460
    Abrasive wear is responsible for large global economic and energy losses, whereas a group of materials, with high toughness and hardness, known as hard metals, is commonly used in situations where this type of wear is dominant. However, these materials are expensive and their susceptibility to corrosion is widely reported in the literature, moreover, in this work, it was shown that these materials are not only subject to degradation due to corrosion, but also that an active liquid with the surface (corrosive) can facilitate brittle fracture. Ceramic materials, which have already shown relative success in abrasive applications, are more cheap, have high hardness and corrosion resistance, despite lower fracture toughness, when compared to hard metals. Thus, in order to carry out a systematic study of these materials when undergoing abrasive wear, ceramic materials and hard metal samples with different percentages of cobalt were characterized in relation to density, hardness, microstructure and fracture toughness via indentation and also tribologically, through mono and multi-event abrasive tests, with test results being correlated with hardness, toughness and the classic Evans and Wilshaw quantity (H1/2 KC 3/4) used to predict the behavior of ceramic materials under this type of wear. As a result, ceramic materials performed better in mild situations, the opposite occurred with hard metals which, considering their greater susceptibility to corrosion and cost, replacing these materials with ceramics in these situations may be viable. The Vickers indenter scratch tests and the dry sand/rubber wheel tests showed reasonable correlations with the fracture toughness via indentation and with the quantity H1/2 KC 3/4. As for hardness, it did not show any correlation with the volume of material removed in any of the tests studied. High data dispersion was observed, therefore, behavior predictions for materials with similar mechanical properties become difficult to make.
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    Superlubricidade no deslizamento de cerâmicos lubrificados com água
    (Universidade Federal do Espírito Santo, 2019-11-22) Strey, Nathan Fantecelle; Scandian, Cherlio; https://orcid.org/0000-0002-4393-719X; http://lattes.cnpq.br/8466752738430250; https://orcid.org/0000-0002-2568-116X; http://lattes.cnpq.br/3613706957012460 ; Sinatora, Amilton; https://orcid.org/0000-0002-5004-4947; http://lattes.cnpq.br/2988437176012972; Souza, Roberto Martins de; https://orcid.org/; http://lattes.cnpq.br/; Bozzi, Antonio Cesar; https://orcid.org/0000-0003-4857-0216; http://lattes.cnpq.br/3017292130810807; Murray, Henara Lillian Costa
    Superlubricity is the state of a tribosystem characterized by extremely low friction coefficients, with μ < 0.01. The superlubricity of ceramic pairs sliding in water has been reported for several similar and dissimilar tribopairs: Si3N4-Si3N4; SiC-SiC, Al2O3-Al2O3, ZrO2-ZrO2, Si3N4-SiC, Si3N4 Al2O3, Al2O3-SiC, ZrO2-SiC, etc. By hypothesis, some requirements must be satisfied for superlubricity in these tribosystems to occur: low enough mean contact pressure, adequate surface finish, a mild wear regime during running-in where tribochemical mechanisms are dominant, and formation of a soft tribofilm adhered to surfaces. These conditions were reevaluated through different approaches: (i) the polishing process parameters were optimized during the preparation of engineering ceramics used in tribological components and a better surface finish was obtained for SiC surfaces when compared to Al2O3 or ZTA ones; (ii) wear maps were developed for several dissimilar ceramics pair sliding in water which showed that the combination of tribologically compatible ceramic counterparts extends the operating conditions range of ceramic sliding bearings and that the mild wear regime is a necessary but not sufficient condition for the occurrence of superlubricity. Finally, (iii) the construction of Stribeck curves for Si3N4-SiC, ZrO2-SiC, Si3N4-Al2O3 and SiO2-SiO2 pairs showed that superlubricity is associated with mixed or hydrodynamic lubrication regime, depending on operating conditions, and that the ratio between the minimum thickness of the hydrodynamic film and the amplitude of the surface roughness peaks (λ ratio) is the parameter that best explains the friction coefficient of these tribosystems.