Influence of sintering process on microstructure and fracture behavior of CF/Si3N4 laminated ceramic composites

Carbon fibre reinforced Si3N4 (C-F/Si3N4) biomimetic laminated ceramic composites were prepared through rolling, alternate stacking of two-dimensional carbon fibre cloth and Si3N4 green layers, burning out of organic components and hot-press sintering. The effects of the sintering process and sintering additives on the microstructure, fracture behavior and toughening mechanism of the composite were analysed. When sintered at 1850 degrees C for 1.5 h with Al2O3, Y2O3 and MgO as sintering additives, a fully densified composite was obtained with homogeneous and moderate bonding interfaces between C-F and the Si3N4 matrix, presenting improved flexural strength of 374.93 MPa and fracture toughness of 10.71 MPa m(1/2), which were increased by 13.20% and 71.36% respectively, as compared with the monolithic Si3N4 ceramic. The primary toughening mechanism of the composite can be concluded as multiple crack deflection at the carbon fibre layers, fracture and pull-out of C-F bundles and single C-F within the carbon fibre layers.