The effect of beam and crystal tilt on quantitative HREM measurememts of grain boundary volume expansion

Abstract

The effects of both beam and crystal tilt on quantitative high resolution electron microscopy (HREM) measurements of grain boundary volume expansion have been investigated. As volume expansion - or rigid body translation normal to a given boundary - has been found to directly vary with the grain boun-dary energy, it is important that accurate measurements of this quantity can be made. The type of measurement we consider is a technique first outlined by Stobbs and co-workers and modified by Merkle. The technique utilizes a linear least squares fit to the centers of gravity of either peak or valley positions in the HREM image. The interplanar distances on both sides of the boundary outside the strain fields of the core are first determined, and the measured width of the boundary region is extrapolated. The volume expansion is then determined as the difference between this measured width and the effective unrelaxed width of an ideal boundary.