Motion of Dislocations in Highly Perfect Copper Crystals

Abstract

Motion of dislocations after their breakaway from as-annealed positions, is studied in highly perfect copper crystals at stress levels less than the shear stress τ_m needed for dislocation multiplication, using an etch-pit technique. The main results are as follows: (i) Waiting time t_w required for the edge dislocation to jump over the obstacle by a thermally activated process, is experimentally shown to range from 3 to 5 s under effective shear stresses of 5.4 to 9.5×10⁴ Pa at room temperature, whose values correspond to the activation energies of about 6∼7×10⁻²⁰ J. Forest dislocations are not responsible for this process. (ii) In contrast with edge dislocations, the initial and final positions (etch-pits on the {111} surface) of moved 30°-screw dislocations are often out of a straight line parallel to ⟨110⟩. This is due to the disappearance of the large super-jog from the {111} surface by its conservative motion under an applied stress. (iii) The distance moved by the edge dislocation is much larger than that by the 30°-screw one.