Characteristic evaluation of liquid phase sintered SiC materials using nondestructive technique

Full text of publication follows: The strength property of liquid phase sintered (LPS) SiC materials has been investigated, based on the detailed analysis of their microstructures and ultrasonic wave properties. The damage behaviors of LPS-SiC materials by the cyclic thermal shock test were also examined by a nondestructive technique using the ultrasonic wave. LPS-SiC materials were fabricated by a hot pressing, using a commercial SiC powder with an average size of about 0.3 μm. The compositional ratios of additive materials (Al2O3/Y2O3) for the densification of SiC materials were changed from 0.3 to 1.5. The compact preform by the mixture of SiC, Al2O3, and Y2O3 particles was sintered at the temperature of 1820 deg. C, which could create the secondary phase like YAG between the SiC grains. The thermal shock test for LPS-SiC materials was carried out at the temperatures of 150 deg. C, 200 deg. C and 250 deg. C. The characterization of all materials was investigated by means of SEM with EDS and three point bending test. LPS-SiC materials represented a good density of about 3.1 Mg/m3 and an average flexural strength of about 750 MPa at an additive composition ratio (Al2O3/Y2O3) of 1.5. The velocity of ultrasonic wave for LPS-SiC materials was constant, even if the specimen had a higher sintered density and the increase of flexural strength. On the contrary, LPS-SiC materials with a higher flexural strength had a lower attenuation coefficient of ultrasonic wave. The damages of LPS-SiC materials by the thermal shock greatly increased with the increase of test temperature, accompanying the creation of large amount of micro-cracks on the surface of the specimen. The efficiency of nondestructive technique for the prediction of material strength is also discussed. (authors)