CHEMISTRY, BONDING AND FRACTURE OF GRAIN-BOUNDARIES IN NI3SI

The chemistry and electronic structure at grain boundaries in B-free a nd B-doped Ni-23 at.% Si alloys were examined, with energy dispersive X-ray spectroscopy (EDX) providing information on the former and elect ron energy loss spectroscopy (EELS) on the latter. Ni-enrichment was s een at large angle boundaries, both in the absence and presence of B. EELS of the Ni L-3 edge showed that the bonding al Ni-rich grain bound aries was similar in both undoped and doped alloys. Comparison of the Ni L-3 edge recorded at the grain boundary and in the bulk suggests th at reduced hybridization and occurs at Ni-rich grain boundaries in bot h doped and undoped alloys. These changes in bonding are interpreted i n terms of changes in the cohesive energy of the boundaries. The relat ionship between the cohesive energy of grain boundaries and the fractu re mode of Ni3Si is discussed. (C) 1997 Acta Metallurgica Inc.