Avaliação e qualificação do uso de tomografia de raios-x no acompanhamento do processamento de compósitos híbridos CRFC/SiC
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2019-12-19
Autores
Souza, Maria Aparecida Miranda de
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Universidade Estadual Paulista (Unesp)
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Compósitos de carbono reforçados com fibra de carbono (CRFC) e compósitos híbridos de carbono e carbeto de silício reforçados com fibra de carbono (CRFC/SiC) são materiais de grande interesse na indústria aeroespacial devido principalmente às suas excelentes propriedades termomecânicas a altas temperaturas. O controle do processo de obtenção desses compósitos realizados por técnicas não destrutivas, tais como a tomografia de raios-X podem apresentar não somente informações relativas à massa específica e porosidade, mas também visão 3D com identificação de poros abertos e fechados e a localização precisa destes e outros defeitos na amostra. Neste estudo, um compósito de matriz híbrida CRFC/SiC, obtido por uma rota alternativa de preparação, baseada em reação de carbono-silício por impregnação direta de silício em pó disperso em resina fenólica, seguido de tratamentos térmicos consecutivos a 1000°C e 1600°C sob atmosfera inerte, teve seu processo reacional monitorado passo a passo, em seus estágios de preparação utilizando difração de raios-X. O desenvolvimento do estudo morfológico do compósito resultante foi realizado utilizando-se duas técnicas de tomografia computadorizada comparativamente à microscopia óptica, sendo esta última técnica já consolidada em trabalhos anteriores, com foco em detecção e quantificação de defeitos. Os três métodos apresentados demonstraram informações satisfatórias para a análise estrutural das etapas de obtenção do compósito CRFC/SiC. A utilização da microtomografia de raios-X, com voxel de 7,4 µm permitiu, além da detecção e quantificação dos defeitos relacionados a poros, o acompanhamento da formação das fases nas diversas etapas de tratamento térmicos, mostrando-se uma excelente técnica complementar à difração de raios-X, permitindo inclusive a visualização de Si sobrante na reação. A utilização de um tomógrafo com voxel de 125µm mostrou-se excelente para verificação de danos entre fases dos compósitos, com análises rápidas e aquisição de imagens em intervalos da ordem de um minuto. As amostras destinadas aos ensaios por tomografia não exigiram preparação dos corpos de prova, apresentando somente limitações de geometria definidas pelo volume das câmaras de ensaios dos equipamentos, além de permitir a reconstrução 3D das imagens. O compósito híbrido CRFC/SiC preparado demonstrou reação total do Si a partir de patamares de 1 hora a 1600°C, apresentando fases β-SiC e α-SiC.
Carbon fiber reinforced carbon composites (CFRC) and carbon fiber reinforced carbon and silicon carbide hybrid composites (CFRC/SiC) are materials of great interest in the aerospace industry due mainly to their excellent thermomechanical properties at high temperatures. Controlling the process of obtaining these composites performed by non-destructive techniques such as X-ray tomography can present not only information regarding density and porosity, but also 3D vision with identification of open and closed pores and their precise location and other defects in the sample. In this study, a CFRC/SiC hybrid matrix composite, obtained by an alternative preparation route, based on carbon-silicon reaction by direct impregnation of silicon powder dispersed in phenolic resin, followed by consecutive heat treatments at 1000°C and 1600°C under an inert atmosphere, the reaction process was monitored step by step in its preparation stages using X-ray diffraction. The development of the morphological study of the resulting composite was performed using two computed tomography techniques compared to optical microscopy, the latter technique already consolidated in previous works, focusing on detection and quantification of defects. The three methods presented demonstrated satisfactory information for the structural analysis of the steps of obtaining the CRFC/SiC composite. The use of X-ray microtomography with 7.4 µm voxel allowed, besides the detection and quantification of pore-related defects, to follow the formation of the phases in the various thermal treatment stages, proving to be an excellent complementary technique to the X-ray diffraction, even allowing the visualization of Si remaining in the reaction. The use of a 125µm voxel tomograph proved to be excellent for verifying damage between composite phases, with rapid analysis and image acquisition at intervals of the order of one minute. The samples destined to the tomography tests did not require the preparation of the specimens, presenting only geometry limitations defined by the volume of the equipment's test chambers, besides allowing the 3D reconstruction of the images. The prepared CRFC/SiC hybrid composite demonstrated total reaction of Si from 1 hour at 1600°C, presenting β-SiC and α-SiC phases
Carbon fiber reinforced carbon composites (CFRC) and carbon fiber reinforced carbon and silicon carbide hybrid composites (CFRC/SiC) are materials of great interest in the aerospace industry due mainly to their excellent thermomechanical properties at high temperatures. Controlling the process of obtaining these composites performed by non-destructive techniques such as X-ray tomography can present not only information regarding density and porosity, but also 3D vision with identification of open and closed pores and their precise location and other defects in the sample. In this study, a CFRC/SiC hybrid matrix composite, obtained by an alternative preparation route, based on carbon-silicon reaction by direct impregnation of silicon powder dispersed in phenolic resin, followed by consecutive heat treatments at 1000°C and 1600°C under an inert atmosphere, the reaction process was monitored step by step in its preparation stages using X-ray diffraction. The development of the morphological study of the resulting composite was performed using two computed tomography techniques compared to optical microscopy, the latter technique already consolidated in previous works, focusing on detection and quantification of defects. The three methods presented demonstrated satisfactory information for the structural analysis of the steps of obtaining the CRFC/SiC composite. The use of X-ray microtomography with 7.4 µm voxel allowed, besides the detection and quantification of pore-related defects, to follow the formation of the phases in the various thermal treatment stages, proving to be an excellent complementary technique to the X-ray diffraction, even allowing the visualization of Si remaining in the reaction. The use of a 125µm voxel tomograph proved to be excellent for verifying damage between composite phases, with rapid analysis and image acquisition at intervals of the order of one minute. The samples destined to the tomography tests did not require the preparation of the specimens, presenting only geometry limitations defined by the volume of the equipment's test chambers, besides allowing the 3D reconstruction of the images. The prepared CRFC/SiC hybrid composite demonstrated total reaction of Si from 1 hour at 1600°C, presenting β-SiC and α-SiC phases
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Compósito Híbrido CRFC/SiC, Microtomografia, Microscopia Óptica, Image analysis, CFRC/SiC, hybrid composite, X-Ray microtomography, Optical microscopy, Análise de imagem, Materiais compostos, Microtomografia por raio-X