MEASUREMENT OF ELASTIC AND ANELASTIC PROPERTIES OF REACTION-FORMED SILICON CARBIDE-BASED MATERIALS

The dynamic Young's modulus and the strain amplitude dependence of damping, at room temperature as well as at elevated temperatures, were determined for reaction-formed SIC (RFSC) ceramics, and the results are compared with those for other SiC materials. The method used was the piezoelectric ultrasonic composite oscillator technique (PUCOT). Five specimens were studied: NC 203 (a commercially produced SIC by Norton, Co.); RFSC No. 1 and RFSC No. 2 (each containing residual Si); RFSC No. 3 and RFSC No. 4 (both containing residual Si and MoSi2). Metallographic observations showed that the microstructure of the RFSC is essentially isotropic with a uniform distribution of phases. The ''rule of mixtures'' calculations cannot be used to predict accurately the elastic modulus of the RFSC, but they can be used to predict the density to within 5%. It was determined that for the RFSC, the dynamic Young's modulus decreases as temperature increases, in a manner similar to that for other SiC materials. It was also found that the damping of the RFSC is generally independent of strain amplitude and is weakly affected by temperature. The activation energy was determined for the change in damping with change in temperature of RFSC No. 2 and RFSC No. 3.