Crack healing in the SiC–SiC ceramic matrix composites fabricated with different process

Abstract

In this study, crack healing in a SiC–SiC ceramic matrix composite (CMC) was investigated. As a gas turbine often operates at a high temperature above 1350 °C and is frequently cooled to room temperature, small cracks that form in the interior of a hot gas component propagate to the surface of the component. Owing to a mechanical constraint condition and dynamic vibrations, stress concentration occurs at the cracks, which grow and eventually reduce the service life of the turbine component. Self-healing technology has been used to solve this problem. We studied the crack-healing behavior of plate-type SiC–SiC CMC samples prepared by liquid melt infiltration (LMI) and cylindrical SiC–SiC CMC samples produced by chemical vapor infiltration (CVI) in an experiment. First, a crack was deliberately formed on the surface of the samples through indentation. Subsequently, the sample was subjected to heat treatment, in which the crack-healing temperature and the healing time were controlled. The crack-healing regions on the surface of the samples were observed using a scanning electron microscope, and the composition of the crack-healing region was analyzed by energy-dispersive spectrometry. While the cracks in the SiC–SiC CMC samples prepared by CVI were healed at 1500 °C, those in the SiC–SiC CMC samples produced by LMI were healed at a lower temperature, 1400 °C, because of the oxidation of residual Si. The four-point bending test was performed at room temperature and a high temperature (1200 °C) on the SiC–SiC CMC samples prepared by LMI, and it confirmed the healing in the samples.