Investigation into early fatigue damage in electrodeposited copper

•The orientation of grown grain is subject to the influence of maximum shear stress.•Fatigue slip lines occur in slip systems with a high Schmid factor.•However, additional factors might influence the formation of slip lines.•Slip lines might occur when there is a large value for geometric parameter.•Geometric parameters were large for crystal that cracked under bending conditions.

Early fatigue damage in electrodeposited copper film was investigated under cyclic torsion and bending. First, the angle between the longitudinal axis and the slip line that occurred at the film surface was measured after a cyclic loading test. The angle was also calculated from the crystal orientation analyzed by using electron backscatter diffraction. The calculated angle agreed well with that obtained from the experimental results. This means that slip lines occur in slip systems with a high Schmid factor. Second, the relationship between resolved shear stress on the direction of slip and the number of cycles to form slip lines was investigated in a torsion test. The number of cycles to form a slip line tended to be controlled not only by the Schmid factor but also by the direction of slip. Finally, the direction of slip was calculated for grain in which a fatigue crack was initiated and we clarified that the fatigue crack tended to be initiated in grain where the direction of slip was inclined from the film surface.