Microstructural characterisation of a Ni?Fe-based superalloy by in situ small-angle neutron scattering measurements

The microstructural evolution at high temperatures was studied in an experimental Ni–Fe-based superalloy DT706 by in situ small-angle neutron scattering (SANS). Modifying the alloy heat treatment to improve the microstructural stability and mechanical properties in Inconel 706 type superalloys has been a significant research goal for many years. The earlier studies of phase transformation relied mostly on optical and electron microscopy investigations of samples that were cooled down to room temperature after the high-temperature exposure. However, the kinetics of γ' and γ'' precipitation is very fast and new precipitation does occur during the cooling phase. So it is unlikely that the high-temperature microstructure is retained at room temperature. In this presentation, we followed the phase transformation in DT706 alloy by studying the microstructural changes occurring at elevated temperatures. The results of in situ SANS measurements are presented. Microstructure examination on differently heat-treated samples by electron microscopy gives complementary information on the phase transformation sequences. The formation and evolution of precipitates are strongly influenced by the cooling rate from the solution to the η stabilization temperature. The microstructure of DT706 alloy can be tuned using the in situ SANS results.