A DISLOCATION MODEL FOR INTERNAL DAMPING DUE TO THE THERMAL-EXPANSIONMISMATCH BETWEEN MATRIX AND PARTICLES IN MICROHETEROGENEOUS MATERIALS

A transient low frequency internal damping, called delta(T), has been observed in various aluminium-based microheterogeneous materials (Al-1 2.8wt.% Si alloy containing large silicon particles, Al/12 vol.% SiC, Al-7075 alloy/15 vol.% SiC). On cooling delta(T) is characterized by a low temperature broad poorly defined maximum. Moreover, delta(T) incr eases with increasing the cooling rate and decreasing the frequency. I t is shown that the observed phenomena are linked with the internal st resses owing to the thermal expansion mismatch between particles and m atrix. Finally, a model based on the movements of dislocations in the vicinity of the interface particle-matrix is suggested to explain the experimental features of delta(T).