Mechanical and dielectric properties of carbon fiber reinforced reaction bonded silicon nitride composites

Abstract

Carbon fiber (Cf) reinforced reaction bonded silicon nitride (RBSN) composites with various amounts of fiber (5, 10, 15 and 20 vol %) are fabricated at 1400 °C using the direct nitridation method. The effect of Cf on the phase formation, microstructure evolution, mechanical and dielectric properties has been investigated. The XRD analysis using Rietveld refinement shows the presence of alpha and beta silicon nitride with a trace amount of tungsten disilicide. Microstructural analyses show the uniform dispersion of Cf in the RBSN matrix and the different toughening mechanisms operated in the composites. Mercury intrusion porosimetry results show unimodal to the multimodal distribution of pores with the increase in the quantity of Cf. The porosity of the composites varies from 30 to 38% with the addition of Cf. The addition of Cf has enhanced the fracture toughness of the composites only with 5 vol % Cf and the maximum toughness achieved is 2.5 MPa m1/2. There is no interface reaction on the Cf, which indicates the stability of fibers in the nitrogen atmosphere at 1400 °C. The dielectric performance of the composites in the X-band frequency range (8.2–12.4 GHz) is found to increase with Cf content.