Near-net-shape fibre-reinforced ceramic matrix composites by the sol infiltration technique

Abstract

The infiltration of a ceramic fibre preform by a ceramic sol is a cost-effective method for the manufacture of ceramic matrix composites (CMCs). The ceramic sol after calcination forms the matrix and the discontinuous fibres act as the reinforcement agents. In this paper, a technique has been presented in which discontinuous mullite preform with 15 vol.% of fibre content was infiltrated with the stabilized zirconia–yttria (ZrO 2·10 wt.% Y 2O 3) sol to fabricate near-net-shape CMCs. The effects of sol viscosity, number of infiltration, in situ deposition of carbon in the CMC samples, and calcination (in air and nitrogen atmosphere) temperature on physico-mechanical properties of fabricated CMCs were examined. The characterization of the preform and the developed CMCs were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD indicated the presence of both cubic (c) and tetragonal (t) zirconia in the CMCs calcined even at 1400 °C. The flexural strength of the CMCs (calcined in air at 1400 °C) when determined by the three-point bend test was found to be almost 14 MPa under a given set of experimental conditions, while calcination of the same materials at 1400 °C in nitrogen atmosphere (carbon-containing CMCs) exhibited a modulus value of almost 51 GPa. SEM indicated multiple fractures of the matrix, which gave rise to pseudo-ductility. This is also evident from the load–elongation curve of the three-point bend test. The reinforced fibres acted as crack arresters, which prevented the propagation of the cracks. SEM studies also indicated fibre pull-out in the fracture surface of the CMCs.