첨단 SiCf/SiC 복합재료의 균열 치유와 초음파탐상 기술의 응용

Abstract

After sintering the SiCf/SiC composite ceramics as material applied to blanket structure of fusion reactor, micro-crack was created by conducting Vickers test. The refraction of the crack was observed by using the SEM and the relation between the bending strength and the orientation of reinforced fiber was analyzed. There is no relation between the bending strength of SiCf/SiC composite ceramics and the size of a pre-crack until the limited crack size. Crack healing behavior was investigated on SiCf/SiC composite ceramics with a coating of SiO2 nano colloid on the surface using various methods, such as dipping and hydrostatic pressure. Although the coating treatment with SiO2 nano colloid is conducted according to the hydrostatic pressure method, SiO2 oxide is not created to the base of a crack. As a result, the recovery of bending strength cannot be anticipated. Nondestructive evaluation (NDE) of ceramic matrix composites is essential to develope reliable ceramics for industrial applications. In this work, C-scan image analysis has been used to characterize surface cracks in SiCf/SiC composite ceramics nondestructively. The possibility of detecting surface cracks was evaluated experimentally using ultrasonic equipment of μ-SDS with a probe of 170 MHz. The defocus method could detect the shape of surface cracks. As a whole, when the defocus method for the probe was used, we conclude that there is a good possibility of detecting surface cracks. It was studied on the nondestructive evaluation of the elastic wave signal of SiC ceramics and SiCf/SiC composite ceramics under monotonic tensile loading. The elastic wave signals of cross and unidirectional SiCf/SiC composite ceramics were obtained by pencil lead method and bending test. The time-frequency method which used by the discrete wavelet analysis algorithm was applied. The time-frequency analysis provides time variation of each frequency component involved in a waveform, which makes it possible to evaluate the contribution of SiC fiber frequency. The results were compared with the characteristic of frequency group from SiC slurry and fiber. Based on the results, if it is possible to shift up and design as a higher frequency group, we will can make the superior material better than those of existing SiCf/SiC composites.