Electron microscopy: probing the atomic structure and chemistry of grain boundaries, interfaces and defects

At the heart of 'dynamic embrittlement' phenomena is the stress-induced seg regation of microscopic quantities of embrittling impurities to fracture su rfaces. Grain boundaries and interfaces are often the natural weak links in a material. The structural and chemical information of such internal inter faces can be probed on an atomic scale using transmission electron microsco py. High-resolution electron microscopy can be used to determine the atomic coordinates of crystalline interfaces. Electron-energy-loss spectroscopy ( EELS) and energy-dispersive X-ray spectroscopy can be performed on any boun dary or defect and can provide chemical information such as composition and bonding. The spatial resolution of EDS is limited by low collection effici ency to around 10 Angstrom. The more efficient signal collection for EELS a llows almost atomic resolution for light elements. EELS fine structure offe rs a fingerprint of the local boundary arrangements, and also insight into the bonding (and possible reactivity) of boundaries and other defects. Over all, electron microscopy can be used to identify the atomistic characterist ics of those interfaces susceptible to dynamic embrittlement. The structura l and electronic information obtained can be used as a starting point for s emi-empirical and ab initio simulations. (C) 1999 Elsevier Science S.A. All rights reserved.