EXPERIMENTAL EVALUATION OF THE INTERPHASE REGION IN CARBON-FIBER COMPOSITES WITH PLASMA-POLYMERIZED COATINGS

A simultaneous improvement of both the fracture toughness and strength of composite materials is very hard to realise. In this study, plasma polymerised HMDSO/O-2 coatings have been deposited onto carbon fibres to provide a distinct interphase and a means of achieving this aim. U tilising a microwave energy source, coatings of various thickness were examined. By carefully controlling the how rate of oxygen into the pl asma, the resultant coating modulus could be selected within the range 0.7-2.0 of the resin modulus. Thus, the technique can be used to achi eve interfacial interlayers with a range of stiffness. The micromechan ics of interfacial failure were evaluated by the fragmentation test. V arious fibre pretreatments (with O-2, N-2, Ar) and coating post-treatm ents (with O-2 and acrylic acid) were also employed. Oxygen plasma pre treatment was found to significantly improve the adhesion of the coati ng to the fibre. (C) 1998 Elsevier Science Limited. All rights reserve d.