Fatigue Strength and Damage Behaviors of Multi-Scale Metallic Films and Multilayers

An understanding of fatigue reliability of thin metal films and multilayers with layer thickness ranging from micrometers to nanometers is becoming more and more important not only due to the rapid development of micro and nano technology, but also because of the demends of the fundamental research interests in small scale materials. In this paper, we will firstly present a couple of new testing methods for fatigue of metallic mutlilayers. Then, the current state in studies on fatigue strength and damage behaviors of thin metal films and multilayers are reviewed. Fatigue strength of the thin metal films investigated previously and that of the Cu-X multilayers measured by us recently were presented. Microscopic characterization of fatigue crack initiation in the thin metal films and the multilayers shows that there exists a significant variation in fatigue damage behaviors with decreasing layer thickness. The relationship between fatigue properties and microstructures of the materials, especially effects of length scale is discussed. The possible research directons about fatigue of metallic multilayers are suggested.