LOW-TEMPERATURE THERMAL CYCLING OF METAL-MATRIX COMPOSITES STUDIED BYTHE ULTRASONIC LOW-FREQUENCY STRESS-COUPLING TECHNIQUE

The ultrasonic low-frequency stress-coupling technique has been used t o study dislocation processes induced by the difference in coefficient of thermal expansion of matrix and particle in an Al/12vol.% SiC comp osite. The attenuation vs. bias stress response was recorded at equall y spaced temperatures ranging from 280 K to 80 K, successively on cool ing and on heating the specimen. The amplitude of the attenuation chan ge varied strongly with temperature, exhibiting a marked maximum aroun d 240 K. Moreover, whatever the temperature, this amplitude was larger on heating than on cooling. These phenomena are explained in terms of dislocation-point defect breakaway and dislocation movements during t he low-temperature thermal cycle.