Influence of heat treatment on grain boundary microstructure in a Ni–16Cr–10Fe–0·022C model material

A nickel based Ni–16Cr–10Fe–0·022C (wt-%) model material has been investigated principally by atom probe field ion microscopy and transmission electron microscopy. The grain boundary structure was modified by applying four different heat treatments of 550, 600, and 700°C for 1 h and 850°C for 5 h. The Gibbsian interfacial excess of boron, carbon and nitrogen segregation to grain boundaries (GBs) was measured after the heat treatments. The segregating elements were unevenly distributed along the GBs, indicating the importance of the internal GB microstructure. In the material heat treated at 700°C intergranular precipitates of Cr7C3, Cr23C6, and Cr2(C,N) were observed. The stability of these carbides is discussed. The heat treatment at 850°C resulted in the formation of Cr7C3only. Indications of oxygen clustering at GBs and at carbide/matrix interfaces were obtained.