High-Frequency Ultrasonic Characterization of Sintered Silicon Carbide

High-frequency 60- to 160-MHz ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90% to 98% of theoretical, average grain sizes ranging from 3.0 to 12.0 μm, and average pore sizes ranging from 1.5 to 4.0 μm. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. The attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size.