Segregation of boron, carbon and nitrogen to grain boundaries in a nickel based model alloy has been investigated using atom probe field ion microscopy (APFIM). The material corresponds to a commercial alloy (Inconel 600), but contains lower levels of alloy additives and impurities. The major composition was Ni-16Cr-10Fe (wt.%). The alloy was solution annealed at 950°C for 10 min, which resulted in a grain size of 20 μ. Subsequently heat treatments for 1 h at temperatures of 550°C, 600°C and 700°C were applied. TEM investigation showed that the heat treatment at 700°C resulted in precipitation of intergranular chromium-rich carbides. The other temperatures were obviously too low and the aging times too short to cause precipitation, since carbides were not observed in the materials heat treated at 550°C and 600°C.

As the grain size was about 100 times larger than the accessible depth of APFIM analysis (≃200 nm), much care had to be taken in preparing samples containing a grain boundary close to the tip apex.