An EELS study of segregation-induced grain-boundary embrittlement of copper

Grain-boundary segregation is a necessary. but not always sufficient, crite rion for intergranular embrittlement of many metals and alloys. The reason why certain segregants induce embrittlement while others are harmless remai ns unclear, but it has been theorized that segregation may be responsible f or local changes in the atomic bonding which, in turn. may produce brittle failure. Recent developments in electron energy-loss spectrometry in the an alytical electron microscope permit correlation to be made between the pres ence of certain segregants and changes in the bonding of the atoms on the g rain boundary. Because the effects in the energy-loss spectrum are small. t he spatial-difference method (equivalent to a first-difference spectrum) is sometimes used to discern the spectral intensity changes. It is important to ensure that this method of processing the data does not induce the chang es in the spectrum that are usually associated with changes in bonding, and this can be demonstrated by experimental comparison of energy-difference a nd spatial-difference spectra. Using direct measurement. as well as spatial -difference techniques. it is demonstrated that Bi and Sb, well-known embri ttlers of Cu, induce consistent changes in the bonding of Cu, while Ag, a s imilar segregant which does not embrittle Cu, produces no detectable change s in the bonding. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Sci ence Ltd. All rights reserved.