Effect of Thermal Cyclic Annealing on the Decrement of Dislocation Density in Copper Single Crystals

Copper single crystals were annealed in order to lower the dislocation density. Dislocation distribution and density were observed using an etch pit technique.Copper single crystals were grown by the Bridgman method in vacuum (∼2×10−5 mmHg) and in Ar gas from electrolytic high purity copper (99.999%). Grown-in dislocation density was 2∼5×105/cm2. Parallelepiped specimens (∼5×5×70 mm) were prepared by cutting and polishing with acid. Their dislocation density increased to ∼106/cm2. Specimens were annealed in vacuum (∼2×10−5 mmHg) by two methods; (1) isothermal annealing and (2) thermal cyclic annealing. In the latter case, a reciprocating furnace was used.The results obtained were as follows; (1) In isothermal annealing, a lot of sub-boundaries were formed and the decreasing rate of dislocation density was small. (2) In thermal cyclic annealing, the dislocation density decreased from ∼106/cm2 to ∼103/cm2, and sub-boundary was not formed. (3) For the specimen grown in Ar gas, the decreasing rate of dislocation density was small.