The inspection of coating thickness uniformity of SiC-coated carbon-carbon (C/C) composites by laser-induced thermal-wave imaging

The coating thickness non-uniformity during fabrication is directly influenced on the thermal protective performance of SiC-coated carbon-carbon (C/C) composite. We demonstrate that thermal-wave imaging (TWI) approach with laser as external stimulation source is successfully employed for the evaluation of thin SiC coating thickness distribution uniformity on the C/C composite substrate. The thermal wave behavior of SiC-coated C/C composite is analyzed by using of two layers 1D heat transfer model based on considering the laser absorption of SiC medium, and the thermal wave phase is dependent on both the SiC coating thickness and excitation modulation frequency. Experimental results confirm that laser-induced thermal-wave imaging (LITWI) can be used to accurately and reliably assess the SiC coating thickness variations, the phase of thermal wave at high frequency (up to 100 Hz) is more valid for evaluating uneven thin SiC coating thickness (up to 20 μm–30 μm) and the modulated frequency of 20 Hz is available for the estimation of thick SiC coating (up to 150 μm) uniformity. In addition the LITWI can also detect small size (about 160–180 μm) pore defects near to the SiC coating bottom surface. A Laser induced thermal-wave imaging (LITWI) method is successfully used to accurately and non-contact assess the uniformity of thin SiC coating thickness (about 20 μm) on the C/C composite substrate, simultaneously, it can also detect small size (about 160–180 μm) pore defects below the SiC coating. [Display omitted]