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

Carbon fibre reinforced Si3N4 (CF/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°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 CF and the Si3N4 matrix, presenting improved flexural strength of 374.93 MPa and fracture toughness of 10.71 MPa m1/2, 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 CF bundles and single CF within the carbon fibre layers.