Thermal Cyclic Annealing of Copper Single Crystals

Copper single crystals grown in vacuum (10−4∼10−5 mm Hg) by the Bridgman method were annealed in vacuum (∼2×10−5 mm Hg) under three conditions; (1) isothermal annealing, (2) thermal cyclic annealing by a moving furnace, and (3) thermal cyclic annealing by a fixed furnace. Changes in the dislocation distribution, dislocation density and length of sub-boundaries with annealing were examined by means of the etch-pit technique.The dislocation density and the length of sub-boundaries were decreased more significantly by thermal cyclic annealing than by isothermal annealing. The effects of thermal cyclic annealing by a moving furnace were of the same order as those of thermal cyclic annealing by a fixed furnace. In a specimen with small subgrains, the effects of annealing were smaller than in a specimen with large subgrains. In copper single crystals with subgrains larger than a few milimeters, the dislocation densities of the order of 105/cm2 could be decreased to ∼103/cm2 by thermal cyclic annealing for more than 100 hr with a period of 15∼30 min.