COMPOSITES SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 61(2001)1079-1082 Oxide/oxide composites with fibres produced by internal rystallis A.A. Kolchin, V.M. Kiiko, N.S. Sarkissyan, S.T. Mileik Solid State Physics Institute of the Russian Academy of Sciences, Chernogolovka, Moscow district, 142432 Russia Received 8 June 2000: accepted 16 November 2000 Sapphire fibres produced by the internal crystallization method were introduced into an alumina matrix. The fibres were coated with pyrolitic carbon to provide weak bonding to the matrix which is expected to enhance the fracture toughness of the material The composite fabrication process exploited a powder-cloth technique Evaluation of the strength and fracture toughness values of the specimens revealed an increase in the fracture toughness of the composites compared to that of the matrix, although the strength is not affected by the reinforcement. The main conclusion is that the internal crystallization-process yields single-crystal fibres suitable for the reinforcement of oxide-matrix composites. C 2001 Elsevier Science Ltd. All rights reserved Keywords: A. Oxides; A. Ceramic-matrix composites; A. Fibres; B Strength; B. Fracture toughness 1. Introduction families of oxides that provide easy cleavage either on some crystal planes or at an oxide/ oxide interface, and The high strength and high creep resistance of mono has led to the idea of using porous oxides as a crack crystalline and eutectic-oxide fibres, and the good oxi- deflector. One such family includes oxides with B-alumina dation resistance of polycrystalline oxide matrices make and magnetoplumbite structures with highly anisotropic oxide-fibre/oxide-matrix composites (OoCs) primary fracture energy that provides mica-like cleavage char candidates for structural application to serve at tem- acteristics [1]. Another family of oxides is that of the ABO4 peratures above 1200 C. As for any brittle-matrix com- composition [2], which includes a number of tungstates posite, the fracture toughness of an OoC is mainly molybdates, tantalates, niobates, and phosphates. The dependent on energy dissipation at weak interfaces in coating of fibres with such oxides is usually being carried the composite microstructure. out by using liquid- phase processes suitable for con- To trigger wider usage of OOCs, three main develop- tinuous filaments. The idea of a porous oxide matrix [3] ments of different degrees of complexity need to seems to work satisfactorily and, what is most impor accomplished tant, it can be used with any form of the fibre material On the other hand, the advance in developing oxide 1uma水 interface fibres for really high-temperature applications by using traditional methods yielding either mono-crystalline or high corrosion resistance, polycrystalline fibres is rather limited. Mono-crystalline 2. a means of generating an appropriate matrix for fibres remain too expensive to be used as reinforcements the ooc is required, and for structural composites and the use of polycrystalline 3. an appropriate fibre is needed. fibres is limited by relatively low service temperatures [3, 4. Hence, the internal crystallisation method (ICM) During the last decade, success in the first two direc- invented in the authors'laboratory [5] and then used to tions has been visible and impressive h fo make oxide fibres [6-8], which requires less energy input interface materials among oxides has revealed two in a real fibre growth process, can be considered as a basis for the production of various single-crystal and Eomt eutectic fibres. Such fibres have been shown to be effec- ail address. mileiko(@ issp ac ru(ST. Miliko) tive reinforcements for metal-matrix composites, yield- 0266-3538/01/ S.see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(00)00233-5
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