THE INTERACTIONS BETWEEN DISLOCATIONS AND POINT DEFECTS STUDIED BY ULTRASONIC MEASUREMENTS DURING A CYCLIC DEFORMATION

Abstract
A new measurement technique has been worked out in order to observe the microscopic mechanisms which control the mobility of the dislocations. In this technique attenuation α and propagation time t of ultrasonic waves are measured in a sample submitted to a low frequency sinusoidal stress. During heating a lot of such Ɗα(σ) and Ɗt/t(σ) curves (~ 300), each measured during one cycle of the stress, have been drawn. These closed curves have some typical shapes which are characteristic of the mechanism controlling the mobility of the dislocations. The typical curves obtained on the presence of a thermally activated double kink generation mechanism are described in an other paper (3). In this paper, a model is developed to explain the shape of these curves in the presence of an interaction mechanism between dislocations and point defects. According to the point defects mobility the possible shapes of these curves can be very different. Each of these predicted curves has been experimentally observed in aluminium and the connection with the low frequency internal friction spectrum has been established.