The Dislocation Motion and Multiplication in Cu Alloy Single Crystals

Abstract

The pre-yield micro-plastic deformation in single crystals of α Cu–Al and Cu–Ni solid solutions was studied at room temperature by means of the etch pit technique. The motion and multiplication of dislocations were detectable from the shape and size of the etch pits. Some of the specimens were deformed in tension at a strain rate of 4×10⁻⁴ sec⁻¹, and others were deformed with a four-points bending jig under a stress pulse of 1 sec. The frictional stress against the dislocation motion of the two alloy systems were calculated from an equation for the dislocation pile-ups with the measurement of etch pit arrays. The “10⁻⁶ yield stress” was studied with a strain indicator with a sensitivity of 2×10⁻⁶ and compared with the result of the etch pit observation.
The dislocation motion was observed under a much lower stress than the yield stress, and the ratio of the number of moved dislocations to that of total grown-in dislocations decreased as the solute concentration increased.
The dislocation multiplication stress detected by the etch pit observation in the bending test was higher than that in the tension test. The multiplication stress corresponded to the “10⁻⁶ yield stress”.
From the observation of etch pits, it was assumed that the multiplication stress corresponded to the stress at which the moved dislocations cut through the forest dislocations.
The frictional stress deduced from the pile-up dislocation arrays increased with solute concentration.