Processamento de compósitos Ni-NbC e Ni-WC pelas técnicas de moagem de alta energia e granulação em tambor

• Ano de defesa: 2016
• Autor(a) principal: Medeiros, Sloany Guedes
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM CIÊNCIA E ENGENHARIA DE MATERIAIS
• Palavras-chave em Português: Níquel; Carbeto; Granulação; Moagem de alta energia; Densidade; CNPQ::ENGENHARIAS::ENGENHARIA DE MATERIAIS E METALURGICA
• Link de acesso: https://repositorio.ufrn.br/jspui/handle/123456789/23537

Nickel matrix composites reinforced by dispersed NbC or WC particles are promising materials due to high mechanical strength and wear resistance. The objective of this study was to evaluate the dilatometric behavior, microstructure and microhardness of Ni-NbC and Ni- WC composites. The composites were obtained by powder metallurgy using high energy milling to provide the dispersion of the hard NbC or WC particles in the nickel matrix. An attritor with speed 850 rpm was used to wet mill and mix the powder mixtures for 2 hours. The powders were prepared with 5%, 10% or 15% (wt.%) of NbC or WC, and subsequently drum granulated. Both granulated and non-granulated powders were uniaxially cold pressed under 600 MPa. The density of green and sintered samples was measured by the geometric method. Microhardness tests and microstructural analyses were performed on the sintered samples. For dilatometric tests, the following conditions were employed: (i) 25°C to 1200°C; (ii) 25°C to 1300°C, both parameters with isothermal step of 1 h and heating rate of 10 °C/min; (iii) 25 ° C to 1200 ° C with isothermal step of 2 h and the same heating rate. The results showed that the sintered nickel samples without addition of reinforcements depicted major densification and high retraction when drum granulated. The SEM images of milled mixtures of Ni-NbC confirmed a certain degree of homogenization and the mechanical incorporation of the ceramic particles in the matrix On the other hand, the results for Ni-WC did indicate non-homogeneity and little mechanical incorporation. The sintered samples of all compositions of Ni-NbC showed higher values of density under sintering conditions (iii), whereas Ni-WC depicted the lowest relative density values. With respect to the images obtained by SEM, the sintered composite with 5% of carbides presented better microstructural characteristics regarding porosity. The Ni-NbC10% and Ni-WC15% composites presented porous microstructure and clusters. The addition of NbC in nickel matrix showed higher microhardness results than the one with WC, although Ni-WC composites showed higher homogeneity.