Preparation of three-dimensional carbon fibre reinforced BN–Si3N4 matrix composites by precursor infiltration and pyrolysis

Abstract

A hybrid precursor was synthesised from borazine and perhydropolysilazane; three-dimensional carbon fibre reinforced nitride composite materials (3D Cf/nitrides) were prepared through vacuum infiltration of precursor and pyrolysis under inert atmosphere. The structures of the hybrid precursor and its pyrolytic products at different temperatures were characterised by fourier transform infrared spectra and X-ray diffraction. The densification behaviour and mechanical properties of the composites and the effects of pyrolysis temperature on their properties were investigated. As the temperature increases, the incidence of B–H, N–H and Si–H groups decreases, even to the point of disappearing, and the d002 spacing of h-BN is reduced, which indicates better crystalline ordering. The main components of the pyrolytic products are BN and Si3N4. On increasing pyrolysis temperature from 800 to 1300°C, the density of the Cf/nitride composites increases from 1˙65 to 1˙69 g cm–3, while the flexural strength increases from 192˙3 to 245˙6 MPa, and the elastic modulus increases from ∼56˙3 to 68˙1 GPa. The load displacement curves show that carbon fibres cause efficient reinforcement, and the composites have good toughness, up to 8˙36 MPa m1/2.