Programa de Pós-Graduação em Engenharia e Ciência dos Materiais
URI permanente desta comunidadehttps://repositorio.ucs.br/11338/46
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2 resultados
Resultados da Pesquisa
- Avaliação mecânica e tribológica de compósitos alumina-nióbio obtidos via sinterização por plasma pulsado(2017-04-10) Bandeira, Aline Luísa; Farias, Maria Cristina More; Machado, Izabel Fernanda; Bergmann, Carlos Pérez; Catafesta, Jadna; Costa, Carlos AlbertoThis work presents a study of the mechanical and tribological properties of niobium-reinforced alumina composites obtained by the spark plasma sintering (SPS) technique. Alumina and niobium powders were characterized regarding the size distribution and morphology of particles by laser diffraction and scanning electron microscopy, respectively. These particulates materials were mixed and simultaneously pressed and sintered by SPS with a uniaxial pressure of 50 MPa at 1400oC. The microstructure and crystalline phases of sintered materials were determined by scanning electron microscopy and X-ray diffraction, respectively. Mechanical properties of the samples related to the stiffness, hardness and fracture toughness were determined by means of the instrumented indentation test and the Vickers indention test. For the tribological study of the ceramic materials, sliding wear tests were performed using the experimental design statistics technique. A factorial design at two levels was used in order to evaluate the main and the interaction effects of three factors – Nb concentration, normal load and counterbody – on friction and wear responses. Empirical relationships between the responses and the interest factors were obtained by means of the factorial design at three levels. Sliding wear tests were conducted in dry environment at room temperature using a ball-on-disc configuration, three levels of normal load (5 N, 10 N and 15 N), ceramic disks with three compositions (alumina, alumina-15%Nb e alumina-25%Nb), metallic (AISI 52100 steel) and ceramic (Al2O3) balls as well. The tribological behavior of the materials was evaluated with regard to friction coefficient, wear coefficient and wear mechanisms. The results showed that composites exhibited an increase in mechanical resistance because they had higher fracture toughness values than the monolithic alumina. In addition, the brittleness index that correlates the stiffness, hardness and the fracture toughness was lower for the composite with a higher niobium content. Statistical results indicated that the main and interactions effects involving niobium concentration and counterbody were significant. The friction coeficiente for the composites was slightly lower for the steel counterbody. When sliding against the steel counterbody composites exhibited a wear resistance two orders of magnitude higher than that of the monolithic alumina and specific wear coefficient values characteristic of the mild wear regime. The higher wear resistance of composites was related to the tribofilm formation over worn surfaces, due to material transfer from the counterbody. Monolithic alumina showed a higher wear in relation to the composites, due to brittle fracture, mostly when sliding against the Al2O3 counterbody at higher loads. The good strength of matrix/reinforce interface contributed to increase the fracture toughness of composites, as well as to prevent the pull out of niobium particles from alumina matrix and to increase the sliding wear resistance of alumina – niobium composites.
- Comportamento do desgaste e posterior corrosão do sistema duplex AISI 4140 nitretado/CrN em bioetanol combustível(2012-09-21) Bandeira, Aline Luísa; Figueroa, Carlos Alejandro; Farias, Maria Cristina More; Sinatora, Amilton; Zorzi, Janete Eunice; Soares, Márcio Ronaldo FariasEste trabalho apresenta um estudo do comportamento tribológico e corrosivo do aço AISI 4140 temperado e revenido, nitretado a plasma e posteriormente revestido com filme fino de CrN, em contato com etanol hidratado combustível. A caracterização das diferentes condições da superfície foi feita por meio das análises de RBS, MEV, DRX, microesclerometria linear e nanoindentação .O coeficiente de atrito foi determinado por meio de ensaios de desgaste por deslizamento tipo esferasobre- disco, em diferentes condições de tratamento do aço AISI 4140 (temperado e revenido, nitretado e duplex) e de lubrificação (a seco, em etanol, em mistura de etanol com óleo lubrificante e em óleo lubrificante). A taxa de desgaste foi estimada por medidas de perfilometria nas trilhas de desgaste. Os mecanismos de desgaste foram determinados com auxílio das técnicas de MEV e EDS, para avaliação microestrutural e química em termos qualitativos das superfícies desgastadas, e da espectroscopia Raman para análise dos compostos químicos presentes. A corrosão foi avaliada por meio de ensaios de imersão em etanol hidratado combustível seguindo a norma NBR 8265, antes e após os ensaios de desgaste. O aço AISI 4140 com tratamento duplex (nitretado/CrN) ensaiado em óleo lubrificante apresentou os menores valores de coeficiente de atrito e de taxa de desgaste. Esse comportamento está associado à formação de um tribofilme composto de óxido de cromo, com elevado potencial iônico, resultante da interação do filme de CrN com o óleo lubrificante durante o contato por deslizamento. A condição duplex apresentou maior resistência à corrosão em relação ao aço AISI 4140 temperado e revenido e ao aço AISI 4140 nitretado.