Microstructures of and crack extension in laminated Si-Ti-C-O fabrics/mullite matrix composites

A sol-gel processed mullite powder of median size 1.7 mum and woven fabrics with 270 mum thick of Si-Ti-C-O fibers (10 vol.%) were formed into laminat ed composites by doctor blade and hot-pressed at 1500-1750 degreesC under a pressure of 39 MPa in a N-2 atmosphere. The structures of fiber interior a nd interfaces between fibers and mullite matrix were characterized by analy tical transmission electron microscopy.: Pyrolysis of the amorphous fibers in dense mullite matrix was suppressed as compared with monolithic fibers w ith no mullite matrix. Partial pyrolysis of fibers during hot-pressing was accompanied by crystallization into beta -SiC, diffusion of Ti element from inside the fibers to the interfaces and the formation of pores inside the fibers. The fracture resistance of the notched composite with crack extensi on was measured at room temperature. A main crack was deflected at the Si-T i-C-O fabric layer under the compressive residual stress, leading to the in crease of fracture resistance near the fabric layer. (C) 2001 Elsevier Scie nce B.V. All rights reserved.