Ductility of Ultra High Purity Copper

Abstract
The ductility of ultra-high purity copper at elevated temperatures was investigated : purity 99.9999% (6N) and 99.999999% (8N). Tensile tests were conducted at temperatures ranging from 293K to 1073K at strain rates of 4.2x10^-5 s^-1 in a high vacuum. The results are discussed in comparison with those for 99.9% (3N) copper. Ductility at intermediate temperatures was improved by an increase in purity. The temperature at which ductility dropped decreased with increases in purity. Even at the ultra-high purity of 8N, a small ductility drop was observed at 423K. A small number of micro voids were observed on the grain boundaries of 8N specimens after the test at 423K. 6N and 8N copper have nearly same sulphur content of about 0.015 ppm. The intermediate temperature embrittlement of these coppers might be affected not only by sulphur content, but also by total impurity content.