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Influence of Nanometer-Scale Multilayered Thin Films on Fatigue Crack Initiation



Mark R. Stoudt, Richard E. Ricker, R C. Cammarata


Fatigue crack initiation in initially smooth, defect free samples of ductile metals almost always occurs at the free surface as a result of surface roughening and the development of a critical surface morphology 1-3. For FCC metals with high stacking fault energies such as Cu, this critical morphology is the result of irreversible dislocation processes occurring during cyclic slip and consists of notches and peaks (intrusions and extrusions) formed at persistent slip bands (PSBs)2,4 as illustrated schematically in figure 1. Recognizing that it should be possible to influence fatigue crack initiation by modifying the properties or microstructure of the surface, investigators have examined the influence of various coatings and surface treatments such as shot peening, anodization, oxidation, nitriding, and ion implantation on fatigue crack initiation. Frequently, the improvement made possibe by these treatments is limited because the cyclic deformation finds another secondary mechanism for the initiation of a fatigue crack. For example, hard coatings effectively prevent surface roughening and fatigue crack initiation until they rupture. Once the coating cracks intense slip results in relatively rapid fatigue crack initiation at the rupture site as illustrated in figure 2 5-7. Since the properties of nanometer-scale multilayered thin film coatings can be modified and adjusted by changing the composition and thickness of the layers, they may allow for optimization of the properties of a coating so that it not only resists the formation of the critical surface roughness, but it gives additional improvement in fatigue life by resisting fatigue crack initiation by secondary mechanisms. The objective of this research was to develop a simple system that would enable testing of the hypothesis that a nanaomter-scale multilayered thin film coating could extend fatigure life and allow for examination of how fatigue crack initiation is modified by coatings with different properties.
Materials Research Society Symposium


crack initiation, fatigue, multilayer, thin films


Stoudt, M. , Ricker, R. and Cammarata, R. (1999), Influence of Nanometer-Scale Multilayered Thin Films on Fatigue Crack Initiation, Materials Research Society Symposium (Accessed April 17, 2024)
Created January 1, 1999, Updated February 17, 2017