Dislocation relaxation in aluminium single crystals at 10 MHz frequency

Abstract

Dislocation relaxation, namely the Bordoni peak, in the three principal planes of a high-purity aluminium single crystal has been studied by measuring the ultrasonic attenuation of longitudinal waves at a frequency of 10 MHz using a conventional ultrasonic single-ended pulse-echo technique. The crystals of <100>, <110>, or <111> orientation were deformed by compression, and the temperature dependence of the ultrasonic attenuation was measured after applying resolved shear stresses ranging up to 60N mm⁻². The results lead to the following conclusions: (i) The temperature of the Bordoni peak is essentially independent of the orientation; (ii) the temperature of the peak decreases up to a resolved shear stress near 28 N mm⁻² and then increases slightly for higher prior stresses; (iii) the peak height increases with increasing deformation; and (iv) a subsidiary peak at the lower temperature side of the Bordoni peak (the Niblett-Wilks peak) appears only at low deformations.