Identification and estimation of defects in high-speed ground C/SiC ceramic matrix composites

摘要

Carbon fibre reinforced silicon carbide (C/SiC) composites are excellent load bearing composites which have additional thermal protection capabilities. Manufacturing and grinding of such ceramic composites without defects is difficult and it eventually affects their loading capacity. The present work proposes means to control grinding induced defects in CVI (chemical vapor infiltration) prepared C/SiC composite by utilizing high-speed grinding. SEM was used to characterize the ground surface morphology. The depth of fibre delamination and defect volume were quantified using an X-ray micro-CT technique. For fibres orthogonal to the ground surface, high grit forces owing to high undeformed chip thickness were found responsible for defect formation. Such fibres contained fibre-matrix delamination up to a depth of 400 mu m from the ground surface. For the other two orientations (with mutually orthogonal fibres in the grinding plane), the grinding scallop and the chip thickness at the machined surface governed the formation of defects. Due to lower grit forces at the machined surface and crack-deflection property of such composites, the defects in the latter orientations remained confined only to the machined surface. High grinding speed of 200 m/s yielded 60% less defects in the composite because of lower grit forces and grit interaction.