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Abstract(s)
Nos últimos anos, a resposta aos desafios de melhoria da eficiência propulsiva nos setores
aeronáuticos e aeroespaciais encontra-se limitada pelas temperaturas de serviço dos materiais.
É cada vez mais imperativo aumentar as eficiências propulsivas das aeronaves em circulação
devido ao seu impacto económico, social e ambiental.
Atualmente a resposta às limitações das superligas metálicas usadas é o seu revestimento
com materiais que permitam o aumento das temperaturas de serviço sem colocar em causa a
integridade estrutural dos componentes e como tal a segurança dos passageiros e das cargas
transportadas.
Com este trabalho propôs-se desenvolver e caracterizar compósitos de matriz cerâmica
contendo na sua matriz zirconato de cálcio e oxido de magnésio, ??????????3 + ??????, em relação
estequiométrica. Esta matriz foi reforçada com diferentes concentrações molares de alumina
(????2??3
), CZM-A10 (10%) e CZM-A20 (20%). Analisou-se o melhor método de formação de provetes
das várias amostras, bem como os melhores ensaios, segundo normas científicas, para a sua
caracterização física e mecânica.
Os materiais foram caracterizados fisicamente através da porosidade e densidade, e
mecanicamente através da dureza de Vickers onde se obteve um incremento máximo de 20%
entre a matriz e o compósito, tenacidade à fratura tendo-se obtido um aumento de 43,8%,
flexão em 3 pontos, cuja tensão máxima de rotura ocorreu na mistura CZM-A20 com o valor de
335,9 MPa e módulo de elasticidade cujos valores apresentam um erro máximo de 1,7% em
relação aos valores teóricos expectáveis. As misturas foram ainda caracterizadas através da
análise microestrutural que serviu de ponte para a perceção dos fenómenos que ocorrem na
estrutura interna durante os ensaios dos provetes.
A adição de reforço foi eficaz, melhorando as propriedades mecânicas da matriz. Duma
forma geral, as melhorias, em termos percentuais, acompanharam o aumento da percentagem
molar do reforço, alumina. Observou-se também a formação de espinela durante o processo de
sinterização. Este fenómeno não tinha sido planificado inicialmente, no entanto permitiu a
conclusão da sua influência na resposta dos compostos aos esforços a que foram sujeitos. As
amostras em estudo foram comparadas com valores da bibliografia e os resultados foram
positivos, visto que existem valores muito próximo dos CMC’s de alta performance.
In recent years, the response to the challenges of improving propulsion efficiency in the aeronautical and aerospace sectors is limited by material service temperatures. It is imperative to increase the propulsive efficiencies of aircrafts in circulation due to their economic, social and environmental impact. Currently the response to the limitations of the metal superalloys used is their coating with materials that allow the increase in service temperatures without jeopardizing the structural integrity of the components and as such the safety of passengers and cargo transported. With this work it was proposed to develop and characterize ceramic matrix composites containing in its matrix calcium zirconate and magnesium oxide, ??????????3 + ?????? in stechiometric relation. This matrix was reinforced with different molar concentrations of alumina (????2??3 ), CZM-A10 (10%) and CZM-A20 (20%). It was analysed the best method of forming specimens of the various samples as well as the best tests, according to scientific standards, for their physical and mechanical characterization. The materials were physically characterized through porosity and density, and mechanically through Vickers hardness, where a maximum increase of 20% was obtained between the matrix and composite, tenacity to the fracture and an increase of 43.8%, flexural strength which the sample CZM-A20 presents the best value, 335,9 MPa, for the rupture strength and modulus of elasticity whose values present a maximum error of 1.7% in relation to expectable theoretical values. The mixtures were also characterized by microstructural analysis that served as a bridge to the perception of phenomena that occur in the internal structure during the tests of the specimens. The addition of reinforcement was effective, improving the mechanical properties of the matrix. In general, the improvements, in percentage terms, followed the increase in the molar percentage of the reinforcement, alumina. The formation of spinel during the sintering process was also observed. This phenomenon had not been planned initially, however it allowed the comprehension of its influence on the response of the compounds to the efforts to which they were subjected. The samples under study were compared with bibliography values and the results were positive, since there are values very close to high-performance CMC's.
In recent years, the response to the challenges of improving propulsion efficiency in the aeronautical and aerospace sectors is limited by material service temperatures. It is imperative to increase the propulsive efficiencies of aircrafts in circulation due to their economic, social and environmental impact. Currently the response to the limitations of the metal superalloys used is their coating with materials that allow the increase in service temperatures without jeopardizing the structural integrity of the components and as such the safety of passengers and cargo transported. With this work it was proposed to develop and characterize ceramic matrix composites containing in its matrix calcium zirconate and magnesium oxide, ??????????3 + ?????? in stechiometric relation. This matrix was reinforced with different molar concentrations of alumina (????2??3 ), CZM-A10 (10%) and CZM-A20 (20%). It was analysed the best method of forming specimens of the various samples as well as the best tests, according to scientific standards, for their physical and mechanical characterization. The materials were physically characterized through porosity and density, and mechanically through Vickers hardness, where a maximum increase of 20% was obtained between the matrix and composite, tenacity to the fracture and an increase of 43.8%, flexural strength which the sample CZM-A20 presents the best value, 335,9 MPa, for the rupture strength and modulus of elasticity whose values present a maximum error of 1.7% in relation to expectable theoretical values. The mixtures were also characterized by microstructural analysis that served as a bridge to the perception of phenomena that occur in the internal structure during the tests of the specimens. The addition of reinforcement was effective, improving the mechanical properties of the matrix. In general, the improvements, in percentage terms, followed the increase in the molar percentage of the reinforcement, alumina. The formation of spinel during the sintering process was also observed. This phenomenon had not been planned initially, however it allowed the comprehension of its influence on the response of the compounds to the efforts to which they were subjected. The samples under study were compared with bibliography values and the results were positive, since there are values very close to high-performance CMC's.
Description
Keywords
Alumina Cerâmica Estrutural Compósitos de Matriz Cerâmica (Cmc) Materiais de Gradiente Funcional (Fgm) Óxido de Magnésio Revestimentos de Barreiras Térmicas (Tbc) Zirconato de Cálcio