A.A. Kolchin et al. /Composites Science and Technology 61(2001)1079-1082 ng an increase in service temperature over Ni-based materials up to about 1150C [9, 10 In the present paper, the prospect of using ICM fibres in oxide-fibre/oxide-matrix composites is shown. The ICM fibres are obtained in the form of either bound or loose bundles of a length up to 200 mm when using existing equipment. Hence, coating processes used for continuous filaments to provide the necessary interface in a brittle-matrix composite are not suitable for ICM fibres. Also liquid-based processes need to be seriously modified to be used with such fibres. and it is clear that coatings produced from a gaseous medium should b tried with ICM fibres In the present work, a somewhat model interface, that is pyrolitic carbon, was chosen ly, mber of ways of generating an oxide matrix can now be used; however, the simplest of these based on a common powder-metallurgy route, is chosen MATRIX since the main purpose of the work is to show the pos FIBRE res duced by ICM in oxide-matrix composites to enhance the fracture toughness of the matrix material 2. Experimental CARBON LAYER 2.1. Preparation of composites 10μM Sapphire fibres produced by internal crystallisation vith the structure and mechanical properties described in detail in Ref [7] were used to make composite speci ptical micrograph of the cross-section of a sapp n(b)a fragment of the failure surface of the com mens. Typically, the fibres are characterised by an aver- posite The scale bar= 10 um. age tensile strength of about 500-800 MPa in tests on samples of I mm gauge length, with a Weibull exponent binder while heating the specimen in vacuum, Fig. la of between 3 and 5. The average characteristic cross-sec On the other hand, during the vacuum treatment the tional size of a fibre is about 0.1 mm. Pyrolitic carboncarbon interface survives perfectly as can be seen in deposited on the fibres from diethylketone by Fig. Ib. Two types of specimens were prepared, both for CVD process. The coating thickness was about 2-3 um. bending tests, Fig. 2, to evaluate the flexural strength Composite specimens were prepared by using a so- and the critical stress-intensity factor called powder-cloth technique, which is well-known as a method of fabrication of intermetallic-based composites 2. 2. Specimen testing (see e.g. Ref. [llD. Thin slurry films containing alumina powder of average size 0.5 um and raw rubber as an The tests were performed at room temperature. The organic binder(powder cloth) were used as a precursor fo strength was evaluated by testing specimens shown in the matrix. The average film thickness was about 160 um. Fig. 2a in 3-point bending. The value of the critical The fibres were arranged on a film of the matrix pre- stress-intensity factor was calculated by testing the spe- cursor by hand. The stack of slurry films and fibres was cimens shown in Fig 2b and using the following inter placed in a closed graphite die, heated in vacuum to polation formula [12] burn out the organic binder, and then sintered under pressure. The temperature-time-pressure conditions were 1350-1400oC, 1-3 h: 70 MPa. The specimen cross- 功1(x) sections are illustrated in Fig. 1. It should be noted that the alumina matrix seems to be saturated with carbon here o' is maximum force and that has not been completely burnt out from the organic x=c/h slurry films were supplied by Drs G.A. Fomina and SD pin of Moscow State University of Aviation Technology, MATl, Ru Y(x)=3√x(1.93-3.07x+14.5x2-251x3+25.8x),    #   # .     ))B'
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