1994 年 43 巻 490 号 p. 847-852
The aim of this work was to investigate the effects of lamination of TiN and Ti2N and prefatigue damage on the fatigue crack nucleation and fatigue life of the steel modified by a dynamic mixing method. The fatigue tests were performed on two types of specimens with or without coating a Titanium film between the laminating film and the steel substrate. The specimens were prefatigued up to 30% and 50% of the fatigue life of substrate. At high stress levels, the laminated films scarcely affected the fatigue life. As the stress level decreased to 250MPa, the fatigue life was improved by laminating the films. Particularly, a thin Ti film between the laminated film and the substrate shorten the fatigue life. The fatigue limit of the laminated specimens increased about 25% more than that of the substrate. The prefatigue damage resulted in a decrease in fatigue life for the laminated specimens. The fatigue crack initiation process depended on the stress range. At high stress levels, cracks nucleated from the film surface. As the stress level decreased, the crack initiation occurred from the interface between the film and the substrate. This change in crack initiation process strongly contributes to the improvement of fatigue life by laminating the films.