A study in the effect of grain boundary on small fatigue crack growth behavior in α-brass by means of in-situ atomic force microscopy

Abstract

The effect of grain boundary on small fatigue crack growth behavior in α-brass was investigated by means of a small in-plane bending fatigue testing machine installed in the stage of an atomic force microscope (AFM). In-situ observation of transgranular fatigue crack growth behavior by an AFM revealed that the small fatigue crack grew along one slip direction with the highest Schmid factor in contrast with the alternating slipping-off crack growth process in a long fatigue crack. A grain boundary worked as a constraint against slip deformation, resulted in frequent crack branching and kinking behavior near the boundary. It was found that the crack growth behavior near a grain boundary was strongly affected by the difference of grain orientations across the boundary. A large number of dislocations were piled up along a grain boundary due to the constraint of slip deformation, which changed the stress state around a crack tip. The newly developed stress distribution activated the slip plane with lower Schmid factor calculated from the nominal stress, and the crack preferentially grew along that plane.