Low-magnification quantitative X-ray mapping of grain-boundary segregationin aluminum-4 wt.% copper by analytical electron microscopy

Quantitative X-ray mapping in the analytical electron microscope (AEM) coul d improve the statistics of grain-boundary segregation measurements if high spatial resolution can be maintained at lower magnifications (<500 WC), Ty pically, only about 10 boundaries are analyzed because of the difficulty of conventional AEM measurements; however, a low-magnification quantitative X -ray map could contain twice this number of boundaries in a single field of view. Microscope conditions and mapping parameters have been explored for operation at similar to 250 kX, under a variety of conditions to illustrate the trade-offs between various characteristics, such as analytical resolut ion, counting statistics, magnification, and acquisition time. From these d ata, it is possible to extrapolate to maps generated under different condit ions and estimate their limitations with respect to these characteristics. A simple model has been developed to describe the behavior of inclined grai n boundaries that can be used to estimate the detectability of segregant as a function of boundary tilt Using quantitative X-ray maps, grain boundary Cu coverage has been measured from 55 boundaries in Al-4 wt.% Cu with minim al user effort. For fine-grained thin films, mapping is substantially more efficient than other methods of data acquisition and may be used to measure segregation at large numbers of boundaries.