SOL-GEL CONTROL OF MATRIX NET-SHAPE SINTERING IN 3D FIBER-REINFORCED CERAMIC-MATRIX COMPOSITES

The origin of thermochemical degradation of 3D reinforced ceramic matr ix composites has been analysed by dilatometry, pore-size distribution and electron microscopy and correlated to the cracking arising from t he matrix shrinkage in an invariant 3D fibre network. The matrix shrin kage of an alumina matrix composite has been delayed zip to a higher t emperature (+200 degrees C) by post-infiltration with pure alkoxide wh ich was subsequently in situ hydrolysed, polycondensed and pyrolysed. Mechanical strength of the composites has been increased four times by optimizing alkoxides. The tensile and flexural mechanical strengths o f these alumina matrix composites are similar to those obtained from S iC matrix composites prepared by the CVI process using the same 3D car bon preform. (C) 1997 Elsevier Science Limited.