Vapour phase preparation and characterisation of SiC f-SiC and C f-SiC ceramic matrix composites

Abstract

Several 2D SiC f-SiC and C f-SiC composites were fabricated using isothermal and isobaric Chemical Vapour Infiltration (ICVI) process. The reinforcements used in the above composites are Nicalon CG fabric and C fabric. Prior to SiC matrix infiltration, BN and C interfaces were applied to the fibre by using the pre-cursors Boron Trichloride (BCl 3)-Ammonia (NH 3) and Methane (CH 4) respectively to improve the mechanical performance of the composites. SiC matrix was infiltrated by the decomposition of Methyl Trichloro Silane-CH 3SiCl 3 (MTS) in the presence of hydrogen at the temperature ranging from 950°C to 980°C. H 2/MTS flow rate ratio used for this study is 16:1.An appropriate temperature for uniform SiC infiltration without any premature pore closures have been obtained by kinetic experiment. Density and porosity of the above composites were measured using the method described by EN1389:2003. Various mechanical characterizations like flexural strength, tensile strength and fracture toughness of the SiC f-SiC composites were also studied. The SiC f-SiC composites were subjected to thermal exposure (1000°C for 100 hr in an oxidizing atmosphere) and tensile strength results obtained before and after thermal exposure were compared. RT Flexural Strength and Fracture Toughness (K IC) of composite-SQAV (SiC f/C/SiC) and composite-SQBII ( SiC f/BN/SiC) are measured by 3-point bending and results were compared. RT Flexural strength of C f-SiC composites with C interface of two thicknesses were measured and compared. X-ray diffraction and micro structure studies have been made to confirm the β-SiC and to see the fibre/matrix interface, uniformity of infiltration, fibre pullout and crack deflections.