On grain boundary dislocations in plane matching grain boundaries

Plane matching (PM) boundaries are defined as boundaries in which a single stack of planes of indices ( hkl ) in each crystal adjoining the boundary is either parallel, or nearly parallel, and where no other significant lattice matching exists. A search is made (by transmission electron microscopy) for possible intrinsic secondary grain boundary dislocation (GBD) arrays which might be present in such boundaries possessing a variety of deviations from the exact PM condition. (002), (220), and (420) PM boundaries of controlled geometry are prepared in gold thin film bicrystal specimens. Wide ranges of twist and tilt deviations from the exact PM orientation are introduced, and the orientation of the boundary plane is also varied for cases of fixed crystal misorientation. Arrays consisting of parallel GBDs are found in the (002) and (220) boundaries but not in the (420) boundaries. The Burgers vector of the GBDs is parallel to hkl with a magnitude given by the ( hkl ) interplanar spacing. Arrays are found in boundaries with twist deviations as large as 4° and tilt deviations as large as 14° and with a wide range of grain boundary plane orientations. The results suggest that discrete GBDs should be present in a variety of (002), (111), and (220) PM boundaries over a considerable range of misorientation which in certain cases may be as large as 20°. Such boundaries should therefore appear rather frequently in general polycrystalline materials in agreement with the estimates of Warrington and Boon. It is pointed out that the physical basis for the stability of such GBD structures is not understood at present.