Fabrication of a NicalonTM fiber/Si3N4-based ceramic-matrix composite by the polymer pyrolysis method

A processing route for ceramic matrix composites is developed based uponpolymer pyrolysis. Three types of NicalonTM fiber woven fabrics,—i.e., uncoated, carbon-coated, and carbon/SiC-coated—are impregnated with apolysilazane solution. Thus-formed prepregs are then cut, laminated,pressed and fired to 1000 °C in a nitrogen atmosphere. Upon pyrolysis,polysilazane converts to a Si3N4-based ceramic matrix with ∼60 wt% yield. The composites made with uncoated NicalonTM fibers have poor flexural andtensile strength (103 and 19 MPa, respectively) and show brittle fracturebehavior. That is due not only to the poor fiber-matrix interface but alsoto processing-induced fiber damage. For carbon and carbon/SiC-coatedNicalonTM fiber composites, the coating layers on the fiber surfacemanipulate the appropriate fiber-matrix interface and also protect thefibers from damage during polymer pyrolysis, so these composites exhibithigher flexural (250 and 274 MPa, respectively) and tensile (138 and 196 MPa, respectively) strength. Also, the load stress-deflection behavior ofcomposites with two types of coated fibers cause noncatastrophic fracture.