The structure of a grain boundary in heat-treated 2.5wt%Nb alloy was studied by means of high-resolution transmission electron microscopy. The orientations of the 2 grains, which were related by a mirror operation about (1¯2▪0), lay within about 2.5º of a (10▪1)[¯10▪2] twin. The boundary was faceted, with coherent terraces lying along the (10▪1) planes in both grains, and with steps parallel to the trace of either (00▪2) or (¯10▪1) in the 2 grains. The steps were 2, 6, 10 or 14 planes in height, and were found to contain a terminating half-plane, in lattice images that were formed by the (10▪1) planes. The observations were explained in terms of Pond's theory of dichromatic patterns for 2 grains in the observed orientation relationship.

The Structure of a Grain Boundary in a Zr-2.5wt%Nb Alloy. G.C.Weatherly, A.Perovic, V.Perovic: Philosophical Magazine A, 1999, 79[9], 2071-82