Repair of SiC coating on carbon/carbon composites by laser cladding technique

A slurry-based laser cladding technique was used to repair the SiC coated carbon/carbon composites. The oxidation resistance of repaired samples at 1773 K for 10 h was investigated. Samples were characterized by X-ray diffraction pattern, scanning electron microscopy and confocal microscope; its interface characteristics were studied with scratch, thermal shock and internal friction tests. The results show that there is no obvious interface between the newly-formed coating and the original coating, and the newly-formed coating has a much smoother surface. With optimizing parameters, the new coating of 180 mu m thickness possesses refined grains, flat surface, dense microstructure and good thermal stability. The number of internal defects in the samples repaired by laser cladding drops, compared with the damaged/undamaged samples. The weight loss of repaired samples decreases by 64.8% in comparison with the damaged ones, and it is almost the same with the undamaged samples according to a test of anti-oxidation behaviors. This is attributed to the enhanced oxidation resistance of dense newly-formed coating, which makes carbon/carbon composites well protected.