Effects of grain boundary characters on the carbide precipitation in Inconel Alloy 600

ABSTRACT The precipitation of carbide at the grain boundary is one of the key factors that influences the resistance of intergranular corrosion. The morphology and growth mechanism of the carbides precipitated at different grain boundaries in Alloy 600 aged at 715°C for different times were investigated by transmission electron microscopy. Two types of carbides, M23C6 and M7C3, can be observed in the sample. The grain boundary character significantly affects the precipitation and distribution of different carbides. The face-centred cubic structured fine M23C6 has a semi-coherent orientation relationship with the matrix, and mainly precipitates at Σ3 grain boundary in all the samples, and at Σ9 grain boundary in the short-term aged samples. The large M7C3 has a hexagonal crystal structure, which does not have typical orientation relationship with the matrix, and precipitates at Σ9 grain boundary in the long-term aged samples, and at Σ27 grain boundary and random grain boundary in all the samples.