Intergranular fatigue crack initiation in polycrystalline copper

Polycrystalline copper specimens were fatigued in strain-controlled regime with high and low strain amplitude. Stress amplitude, plastic strain amplitude and hysteresis loops were recorded. The loop shape parameter reflecting the onset and evolution of the localization of cyclic plastic deformation was evaluated. Mechanism of intergranular fatigue crack initiation was studied on the electrolytically polished specimen surfaces using scanning electron microscopy coupled with focused ion beam. Intergranular cracks had initiated already at 4% of the fatigue life. Corrugated surface of grain boundary cracks close to the surface of the grains was closely related to the occurrence of the extrusions and intrusions produced on the grain boundaries. The observations give further support to the novel mechanism of grain boundary crack initiation based on the emergence of extrusions and intrusions on the grain boundary surface. Factors affecting the initiation of grain boundary cracks were identified.

Automated summary

In this study, the fatigue behavior and initiation mechanism of intergranular cracks in polycrystalline copper specimens were investigated. Scanning electron microscopy was used to observe the crack formation on the electrolytically polished specimen surfaces, and a correlation was found between the occurrence of extrusions and intrusions on the grain boundaries and the formation of corrugated surface near the intergranular cracks. These findings contribute to a better understanding of the fatigue behavior and initiation mechanism of intergranular cracks in polycrystalline copper.