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 μm and woven fabrics with 270 μm thick of Si–Ti–C–O fibers (10 vol.%) were formed into laminated composites by doctor blade and hot-pressed at 1500–1750°C under a pressure of 39 MPa in a N2 atmosphere. The structures of fiber interior and interfaces between fibers and mullite matrix were characterized by analytical transmission electron microscopy. Pyrolysis of the amorphous fibers in dense mullite matrix was suppressed as compared with monolithic fibers with no mullite matrix. Partial pyrolysis of fibers during hot-pressing was accompanied by crystallization into β-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 extension was measured at room temperature. A main crack was deflected at the Si–Ti–C–O fabric layer under the compressive residual stress, leading to the increase of fracture resistance near the fabric layer.