Analysis of slip propagtion across grain boundaries using TEM, anisotropic elasticity, and FEM techniques

The quantitative TEM characterization of lattice dislocation pile-ups at grain boundaries in polycrystalline materials can provide detailed information about the crystallography and mechanisms of slip transmission across a particular interface. This is used as input data in anisotropic elastic calculations of the local stress field and forces on both sides of the interface, and gives pile-up obstacle stresses varying from 280 to 870 MPa for different boundaries in the same type 304 stainless steel sample. These calculations have also led to an improved criterion for predicting slip systems activated across an interface; a double-ended pile-up interacting with two different boundaries is used as an illustration. In addition, dynamic in situ straining experiments in the HVEM reveal mechanisms for dislocation generation not predicted from static TEM studies. Finite element modeling (FEM) is also being used to predict the complete stress and state of specially oriented bicrystals