The detection of the periodic structure of high-angle twist boundaries

Abstract

High-resolution electron microscopy was used to image directly the 0-lattice of 〈001〉 twist boundaries with misorientations up to 25° and 0-lattice spacings as small as 7 Å. The results were entirely consistent with the conclusions reached on the basis of the diffraction experiments described in Part I. An experimental method was devised for determining whether the 0-lattice was imaged by conventional diffraction strain contrast or by interference strain contrast which arises from interference between f.c.c. and 0-reflections resulting from the periodic structure of the boundary (Part I). It was demonstrated that spacings down to about 34 Å were imaged mainly by means of diffraction strain contrast, while networks with spacings of about 16 Å or less were imaged mainly by means of interference strain contrast. Efforts were also made to detect secondary grain boundary dislocation networks, and such networks were observed in the vicinity of the Σ = 5 boundary over a slightly larger range of misorientations than had been detected previously.