The investigations of phase boundary in metallic composites reinforced with carbon fibres
Ignacy Łosik, Zbigniew Zarański, Zbigniew Bojar Wojskowa Akademia Techniczna, Instytut Materiałoznawstwa i Mechaniki Technicznej, ul. Kaliskiego 2, 00-908 Warszawa
Annals 2 No. 5, 2002 pages 333-337
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abstract The results of technological attempts at obtaining of Al-based metal matrix composites reinforced with continuous carbon fibres are shown in this paper. The main purpose of this work was to obtain composite wire by pulling a carbon roving (covering about 6000 elemental filaments) through a liquid Al-Si alloy at conditions securing for full infiltration process. Investigations were conducted changing the temperature and time of infiltration process (by changing the velocity of pulling the roving through liquid matrix), as well by changing the condition of elemental filaments surface (filaments in raw condition, filaments provisionally modified, filaments modified in situ) and changing the composition of liquid matrix (silicon, aluminium, Al-Si alloys). Two different ways for resolving the issue of carbon fibre surface modification, in order to secure the best moistening and to minimise a harmful chemical reactions in aluminium-carbon system were proposed taking into account that the possibility of controlling a phenomenon at filaments/matrix border is critical for obtaining a correct structure and high properties of Al-based metal matrix composites. First of them was provisionally modification of filaments surface by saturating a roving with silicon resin solution and then, heating them at the temperature of 1550oC for 30 minutes. It resulted in creating of SiC barrier coating on filament surface (by diffusion and reactions in solid state). Such modified roving was subjected to effective infiltration process with AlSi11 alloy at the temperature of 1350oC. After them quite weak geometrical effects of interactions at the components boundary zone were observed (Fig. 1c), while a comparative attempts at infiltrating the roving in raw condition (HMS 5236 roving after heating to remove polymeric preparation) confirmed (Fig. 1a, b, as well Fig. 2b) that in the same conditions of process a very distinct effects of chemical reactions in carbon fibre - matrix system (up to fully degradation of elemental filaments (Fig. 1a, Fig. 2b) zone at roving surface in left microstructure) were present. The second of offered processes covers a stage by stage infiltration of roving in raw condition. HMS 5236 roving after provisional heating was pulled through liquid silicon at the temperature of 1450oC and full infiltration effect (probably with SiC barrier coating on filament surfaces growing in situ as results of diffusion and chemical reactions in liquid state) was easy obtained (Fig. 2a). Such provisionally prepared roving was pulled through liquid aluminium bath and silicon matrix was exchanged fir Al-Si alloy matrix with different level of silicon contents (up to neareutectic alloy - Fig. 2c) at the temperature not exceeding 1000oC. The AlSi-continuous carbon fibre composite wires were about 0.6 mm in diameter and a few dozen millimetres in long and had about 80% volume contents of carbon fibres with highly regular cross section geometry (Fig. 2c - right microstructure), evenly distributed in Al-Si matrix (Fig. 2c - left microstructure). It was stated that final efficacy and technological usefulness estimation of barrier coatings obtained by provisional modification process or by in situ modification process could be possible after lasting investigations of components border microstructure and mechanical properties of composite AlSi-continuous carbon fibre wire.