Grain boundary precipitation and segregation in Ni16Cr9Fe model materials

Grain boundaries in a nickel based model material resembling Alloy 600 have been studied using atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM). The grain boundary structure was modified by applying different heat treatments. The solubility of carbon is low in the NiCrFe matrix, therefor carbon segregates to grain boundaries where precipitation follows, depending on heat treatment temperature and time. In the investigated material, boron and nitrogen were also found to segregate. The Gibbsian interfacial excess has been calculated for C, B and N after different heat treatments. Tomographic atom probe (TAP) analysis was used to investigate an intergranular carbide. In the same grain boundary, an adjacent carbide was analysed by conventional atom probe (AP). The results obtained from these two techniques were in good agreement. This shows that the ability to detect multiple ions is satisfactory in this type of three dimensional atom probe.