Quantitative measurements of stresses at grain boundaries in polycrystalline metals

Abstract

It has long been recognized that the deformation of polycrystalline metals proceeds by the movement of individual dislocations both within the grains and across the grain boundaries which separate them. It is known, for example, that the yield stress is directly affected by the density of grain boundaries in a metal; in the familiar Hall-Petch relationship it is inversely proportional to the grain diameter. Various models have been proposed to account for this behaviour, all of which involve the interaction between dislocations and grain boundaries (for a review see e.g. ref. 1). Microscopically, these interactions can be accomplished by several different mechanisms, which include the nucleation of new dislocations, direct transmission of dislocations across the interface, the absorption and desorption of dislocations into and out of the interface.The TEM can be used for both static and in-situ dynamic studies of these interactions. In the static mode, a TEM is used to analyze fully the crystallography of dislocation pile-up/grain boundary interactions; one such pile-up is shown in Fig. 1.