Quantitative compositional mapping of Bi segregation to grain boundaries in Cu

The segregation of impurities and subsequent embrittlement of grain boundar ies in metallic alloys is an important and extensively studied phenomenon. X-ray compositional mapping in the analytical electron microscope (AEM) can identify, quantify and determine the distribution of the segregating eleme nts. This approach offers the advantage over surface sensitive techniques t hat the sample does not have to be fractured, which permits a more complete description of the distribution of the segregant to be obtained. Optimizat ion of a dedicated 300 kV, field-emission gun, ultra-high vacuum scanning t ransmission electron microscope allows the acquisition of compositional map s at high spatial resolution and high sensitivity. Bismuth segregation to g rain boundaries in Cu has been mapped with a spatial resolution better than 2 nm and a sensitivity better than one tenth of a monolayer. Some of the a dvantages of mapping over traditional fixed probe or profile approaches hav e been demonstrated and a survey of segregation levels in a number of bound aries has illustrated the large degree of anisotropy in segregation levels beyond that revealed by surface techniques. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.