In the present study, fiber‐matrix compatibility in an all‐oxide ceramic composite is examined. Reaction‐bonding aluminum oxide is used as porous matrix to ensure weak interfaces with fibers. Matrix cracks have been deflected around the interface for sintering temperatures up to 1300°C, due to the effectiveness of porous matrix in enabling damage tolerance. Above 1300°C, densification of the matrix resulted in brittle fracture of the samples, with matrix cracks going through the fibers. Observation of fracture surfaces confirmed the fiber pull‐out phenomenon up to processing temperatures of 1300°C. The well‐known He and Hutchinson criteria for crack deflection was used to predict debonding behavior at the fiber‐matrix interface as a function of matrix porosity. Furthermore, evaluation of the microstructure evolution of Nextel™ 610 alumina fibers showed a pronounced grain coarsening at sintering temperatures above 1300°C. Changes in crack deflection behavior and fiber microstructure of a composite sample aged for 100 h are also presented.

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Ceramic matrix composites (CMCs) were developed to overcome the intrinsic brittleness and lack of reliability of monolithic ceramics. Their major advantages include high temperature capability, light weight, corrosion resistance and adequate damage tolerance. All-oxide Ceramic Matrix Composites (OCMCs) offer essential advantages with respect to long time stability in oxidizing atmospheres, when compared to their non-oxide counterparts. Nevertheless, there is at present almost no production concept which meets the requirements in view of cost and performance for these materials. This work aims at producing OCMCs by means of a more flexible production route. This is achieved by integrating well-known powder metallurgy routes with the prepreg technique, used at present for producing commercial high performance polymer matrix composites. The processing consists of the following steps: (a) infiltration of commercial alumina fiber fabrics (3M NextelTM610) with a liquid suspension of the matrix material; (b) lamination of the pre-infiltrated fiber textiles with a paraffin-based suspension for the formation of prepregs; (c) layup of prepregs; (d) warm-pressing for the consolidation of the green body; (e) debinding and (f) reaction bonding and/or sintering for synthesis of the oxide matrix. Pure alumina or Reaction Bonded Aluminum Oxide (RBAO) can be used as matrix materials and damage tolerance is achieved by the porous, weak-matrix approach. Microstructural analysis of a pure alumina composite fabricated by this route show good infiltration of fiber bundles and proves the good adhesion of prepregs during processing. Average strength value of 199 MPa in fiber direction is in good agreement with values presented in the literature for OCMCs produced by other techniques.

RESUMOO uso de cerâmicas estruturais é limitado por sua fratura frágil. Compósitos de matriz cerâmica (CMCs) são materiais que possuem reforços estruturais que atuam aumentando a energia necessária para que o material se frature. O presente artigo apresenta uma alternativa para a produção de CMCs em que matriz e fibras são constituídas de alumina. Os mecanismos responsáveis pelo aumento da tenacidade ocorrem devido a uma interfase porosa entre matriz e fibras.Palavras chaves: Compósitos de matriz cerâmica, interface fibra-matriz, ponteamento de trincas. Weak interfaces in alumina/alumina CMCs ABSTRACTThe use of structural ceramics is limited by their brittle fracture behavior. Ceramic matrix composites (CMCs) are materials with structural reinforcements which increase the necessary energy to fracture the material. This paper presents an alternative to produce CMCs possessing matrix and fibers that are made with alumina. The toughening mechanisms occur due to the existence of a porous interface between the matrix and the fibers.Keywords: Ceramic matrix composites, fiber-matrix interface, crack bridging. INTRODUÇÃOCompósitos de matriz cerâmica reforçados por fibras são materiais desenvolvidos para contornar a fragilidade e a baixa confiabilidade das cerâmicas monolíticas. As fibras conferem uma maior tolerância ao dano, tornando esses compósitos aptos a aplicações extremas em que sejam requisitadas altas temperaturas de operação, baixa densidade, resistência à corrosão e tolerância adequada ao dano [1][2][3][4][5][6][7][8][9][10].A natureza da interação entre matriz e fibras é fundamental para os mecanismos de tenacificação responsáveis pelo aumento na resistência mecânica dos CMCs. Interfaces fortes tornam as fibras susceptíveis à propagação das trincas durante a fratura da matriz. Interfaces fracas favorecem a integridade das fibras. Portanto, os compósitos mantêm alguma resistência mecânica mesmo com a fratura da matriz, graças aos mecanismos de tenacificação como deflexão da trinca (crack deflection) e arrancamento (pull out) da fibra.O objetivo do presente artigo é testar a eficiência de uma alternativa para a produção de CMCs alumina/alumina, na qual a porosidade próxima as fibras seja responsável por garantir uma interface fraca capaz de permitir a ocorrência dos mecanismos de tenacificação. CONSIDERAÇÕES TEÓRICASA tenacidade nos materiais cerâmicos é afetada pela microestrutura e pelo caminho que a trinca se propaga pelo material. O caminho de propagação das trincas determina a superfície de fratura gerada, que influência a energia absorvida durante a fratura. Para um material de mesma composição e livre de defeitos, monocristais e vidros possuem uma tenacidade à fratura menor quando comparados aos policristais. Isso pode ser explicado pela maior área de superfície criada na fratura intergranular nos materiais policristalinos [11].O mecanismo de deflexão de trincas, apesar de não contribuir significativamente para o resultado quantitativo da absorção de energia durante a fratura, permite que as estruturas ...

For advanced ceramic composites, affordable manufacturing is still the most essential shortcoming with respect to successful commercial use. This holds particularly for components made out of composites with complex hierarchical structures and high demands of mechanical performance and reliability at the same time, e.g. fiber-reinforced ceramic matrix composites (FRCMCs). Therefore, a new processing route is presented here, which is based on the lamination of thermoplastic prepregs. This route allows not only affordable manufacturing, but also advanced mechanical reliability. Powder metallurgy techniques are combined here with concepts from the prepreg technology in a route consisting of the following steps (a) manufacturing of 2 D prepregs using commercial fiber fabrics which are infiltrated with compounds of ceramic particles embedded in an organic matrix, (b) followed by respective stacking and joining, (c) burn out of the organic matrix and (d) sintering to consolidate the matrix. Composites consisting of a porous Al2O3/ZrO2 matrix, reinforced by 8 layers of NextelTM 610 fiber fabric exhibit a bending strength of ~440 MPa, with graceful failure behavior, e.g. a stepwise stress reduction after peak nominal stress. The fracture of these composites is controlled by a series of interfacial delamination events, which enhance energy dissipation during failure.