Ultrasonic attenuation and velocity data on aluminum single crystals as a function of deformation and orientation

Abstract

Aluminum single crystals oriented for single slip and for “polyslip” were deformed in tension, at room temperature. These tests were limited to a total tensile strain of up to 1 per cent. Simultaneous measurements of attenuation and velocity changes were made continuously during the tensile deformation. Both longitudinal and shear waves were used, at frequencies of 10 Mc/s and 13 Mc/s. The observed changes in attenuation in the polyslip orientations were consistent with an explanation based on the number of equally favored slip systems in each case. The results on crystals oriented for single slip indicate that in the easy glide range of strain hardening, dislocation multiplication is confined to the primary slip system only. The end of easy glide is associated with dislocations multiplying in other slip systems. An increase in attenuation is also observed prior to the onset of the macroscopic yield. This increase is presently attributed to an increase in dislocation loop length, caused by a breakaway mechanism. In the early stages of deformation, for all orientations, an increase of ultrasonic velocity, relative to the unstrained condition, is observed. The changes of attenuation and of velocity reported here, are consistent with theoretical results derived from the treatment of dislocation damping given by Granato and Lücke.