9530314 King This project combines theory and experiment in a study of the effects of free surfaces and triple junctions upon grain boundary structure, properties and behavior. Traditional approaches to grain boundary properties rely on models that are intrinsically infinite, and relatively little attention has been paid to the effects associated with the non-infinite extent of real interfaces. Calculations are made of the elastic fields of grain boundaries made up of dislocation arrays in finite materials, taking into account surface relaxation effects. The effects of free surfaces on the dislocations are considered with a view towards understanding how dislocations are eliminated from grain boundaries, resulting in changes of misorientation. These effects are also studied in polycrystalline films using in-situ transmission electron microscopy experiments which are compared to the calculations. The project includes a study of the properties and behavior of triple junctions within polycrystalline materials. For certain classes of materials, notably thin films, triple junctions may fall into restricted symmetry classes in which the anisotropy of the grain boundary energy exerts a controlling influence on the morphology of the triple line. An attempt is made to demonstrate that these triple junctions embody strain fields and excess elastic energies which depend upon the misorientations of the grain boundaries in calculable ways. This represents a new approach to triple line studies. %%% The overall thrust of this project is to study how the terminations of grain boundaries affect their properties and behavior. This is important in polycrystalline thin films used in electronic applications and in the properties of nanocrystalline materials. ***
