Annealing in slip bands in copper fatigued at 90°K

The hardening of copper single crystals by fatigue

Copper single crystals have been subjected to alternating stresses of such magnitude as would cause complete fatigue failures in 5 x 105 cycles. Slip striations are produced both at 78 and 293 °K and plastic deformation starts in these regions if partially fatigued specimens are extended. In specimens fatigued at 293 °K the material between striations begins to deform at a significantly higher stress than the maximum stress applied during fatigue and yield point phenomena are observed. The flow stress of the yield extension has a strong temperature dependence. Yield point phenomena are less pronounced in specimens fatigued at 78 °K and additional hardening can be produced in such specimens if they are warmed after fatigue to temperatures higher than 200 °K. These observations suggest that point defects make a substantial contribution to the hardening which is observed during fatigue tests at room temperature.