SIMS/AEM Characterization of Banded Microstructures in an Ni-Cr-Fe Alloy

Abstract Ni-Cr-Fe alloys such as Alloy 600 and Alloy 690 are single phase fee alloys with excellent resistance to corrosion. Alloy 600 is generally used in a thermally-treated condition which is characterized by the intergranular precipitation of Cr-rich M7C3 and, depending upon the aging temperature, Cr-rich M23C6. These alloys are usually cast and processed by rolling or forging. These alloys can exhibit microstructures in which there are nonuniform distributions of intragranular carbides that appear as bands aligned parallel to the working direction (i.e. longitudinal) of the material. It is also possible for these materials to exhibit duplex grain sizes which can be associated with the banded carbide structure. Banded microstructures can become more prominent after further anneals. The resistance of the carbide bands to dissolution during solution annealing at temperatures up to 1150°C has prompted the further evaluation of banding in Alloy 600, specifically in terms of identifying those elements associated with the carbide bands.