The role of grain boundary compatibility in fatigue cracking of aluminum bicrystals

The effect of grain boundaries on the cyclic deformation and fatigue crack growth in aluminum bicrystals has been studied. The incompatible primary slip by the two sides of a grain boundary creates heterogeneous slips in a narrow area beside the boundary and cracks along the boundary. The area, termed as Grain Boundary Affecting Zone (GBAZ). is characteristic of heterogeneous deformation as well as internal stresses. As an extended stage I crack grows into the GBAZ under constant cyclic stress, the crack branches and splits deviating from the favorable crack path along a primary persistent slip band (PSB). at the same time, it decelerates or even stops to grow. The microstructure-sensitive growth behavior of extended stage I cracks across grain boundaries in aluminum bicrystals accompanying the crack tip sheilding in GBAZs is refered to the compatibility requirement at the boundaries.