Low-temperature thermal cycling of metal-matrix composites studied by the ultrasonic low-frequency stress-coupling technique

Abstract

The ultrasonic low-frequency stress-coupling technique has been used to study dislocation processes induced by the difference in coefficient of thermal expansion of matrix and particle in an Al/12vol.% SiC composite. The attenuation vs. bias stress response was recorded at equally spaced temperatures ranging from 280 K to 80 K, successively on cooling and on heating the specimen. The amplitude of the attenuation change varied strongly with temperature, exhibiting a marked maximum around 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 the low-temperature thermal cycle.