COMPLEX INTERACTION MECHANISMS BETWEEN DISLOCATIONS AND POINT-DEFECTSSTUDIED IN PURE ALUMINUM BY A 2-WAVE ACOUSTIC COUPLING TECHNIQUE

Ultrasonic experiments using a two-wave coupling technique were perfor med on 99.999% pure Al in order to study the interaction mechanisms oc curring between dislocations and point defects. The coupling technique consists in measuring the attenuation alpha of ultrasonic waves durin g low-frequency stress cycles sigma(t). One obtains closed curves Delt a alpha(sigma) called ''signatures'' whose shape and evolution are cha racteristic of the interaction mechanism controlling the low-frequency dislocation motion. The signatures observed were attributed to the in teraction of the dislocations with extrinsic point defects. A new inte rpretation of the evolution of the signatures measured below 200 K wit h respect to temperature and stress frequency had to be established: t hey are linked to depinning of immobile point defects, whereas a therm ally activated depinning mechanism does not fit the observations. The signatures measured between 200 and 370 K were interpreted as dragging and depinning of extrinsic point defects which are increasingly mobil e with temperature.