Measuring rigid shifts at interfaces by HREM

Abstract

The interfacial energy of an internal interface between two solid crystals can be lowered by local atomic relaxations. In addition to such short-range atomic readjustments, the microscopic displacement of the crystals relative to each other, the rigid-body translation, has been known to provide a major relaxation mechanism for the minimization of grain boundary (GB) energy. In particular, the component normal to the interface, the volume expansion, has been directly linked to GB energy, as suggested more than 30 years ago by Seeger and Schottky. More recently, detailed atomistic computer simulations by Wolf have shown a roughly linear relationship between GB energy and volume expansion for a wide range of GB geometries in metals. In ceramic GBs the relationship between volume expansion and energy is less well established theoretically. For these reasons, and also because of possible direct connections of GB excess volume to a range of GB properties, such as segregation, intergranular fracture, and GB diffusion, experimental measurements of GB volume expansion is an important task of electron microscopy.