Comparison of the number densities of nanosized Cu-rich precipitates in ferritic alloys measured using EELS and EDX mapping, HREM and 3DAP

In this paper we compare various microscopy methods which are used to characterize Cu-rich precipitates in pressure-vessel steels. EELS and EDX mapping is found to reveal Cu-rich precipitates of sizes greater than about 1-2 nm, both those with the bcc structure, which are coherent with the ferrite matrix, and incoherent transformed precipitates. This allows a direct comparison with results from 3DAP, which so far has been the only way to image such ultra-fine Cu-rich clusters. In HREM images only incoherent precipitates which have transformed to a twinned 9R structure are seen. A comparison is made of precipitate number densities and sizes as measured by EELS and EDX mapping, 3DAP and HREM. (c) 2006 Springer Science + Business Media, Inc.