Abstract
Fatigue crack propagation experiments of approximately 500-nm-thick freestanding single crystalline copper (Cu) films were conducted to clarify the intrinsic mechanisms of fatigue crack propagation excluding the effect of microstructure such as twin boundaries in nano-films. A fatigue crack started to propagate stably from a single side edge notch by applying cyclic loading, and the fatigue crack propagated on oblique direction corresponding to the slip systems. Field emission scanning electron microscope (FESEM) observations of the vicinity of the crack and fatigue fracture surface indicated that fatigue damage penetrating the film in thickness direction formed. In addition, thin strips projecting in out-of-plane directions formed along the fatigue crack. In order to clarify the morphology by the fatigue damage, cross-sectional analysis of the fatigue damage ahead of the crack tip was conducted by using a focused ion beam. FESEM observation of the cross-section of the fatigue damage confirmed that instrusions/extrusions formed ahead of the crack tip. This suggests that intrusions/extrusions play a major role in fatigue crack propagation even in single crystal Cu films.
