Dislocation Motion in Copper under Small Stresses

Dislocation motion in copper was studied by dislocation-etching before and under loading, and also after unloading.Parallelepiped copper single crystals had a dislocation density of approximately 1×103/cm2 after thermal cyclic annealing. The dislocation etching under load was accomplished by hanging a small weight on the specimen in the etching solution.Principal results are as follows:(1) Dislocation locking stress due to impurity atoms was estimated to be less than 0.46 g/mm2, assuming that impurity atoms act only as pinning points.(2) Lattice frictional stress for dislocation motion was evaluated to be, at most, 0.20 g/mm2, from the consideration of force balance on a bowed-out dislocation near the crystal surface.(3) Both grown-in and multiplied dislocations were observed to move backward by unloading. Fresh dislocations made a back motion more easily.(4) From an examination of the distance of dislocation motion and the average distance between grown-in forest dislocations, it is suggested that the main obstacle to moving dislocations is forest dislocations.