Copper bicrystals with isoaxial  twist boundaries and a (149)/(001) "random" boundary were notched at the interface, left or right regarding the slip geometry, and intergranular cracks were propagated under strain control, to study how dislocation structure, crystallography and strain localization affect crack growth. Forward slip at the crack surface was favored regardless of growth direction or misorientation, whereas pre-existent multiple slip around the boundary reduced the dependence of crack kinetics on the growth direction. A model is proposed for intergranular crack growth based on crack tip deformation via crystallographic slip bands and simplifying assumptions about the effects of mode I stress fields on the strain. The experimental and theoretical results, along with published data, provide evidence that an optimal slip geometry exists for fatigue crack propagation. This idea is used to explain experimental results on directional dependence of intergranular cracking of bicrystals, suggesting that the kinematics of deformation has to be considered besides the energetics of dislocation nucleation at a crack tip to explain such results.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys