Abstract INCONEL 706 is a superalloy mainly used for very large gas turbine components. Its microstructure is composed of γ ′ and γ ″ as hardening phases and η phase for some applications to control grain size and to improve creep rupture life. Electrical resistivity could be used to study η phase precipitation kinetics in this kind of alloy. It is a method of in situ phase transformation analysis which proved to be efficient to study microstructure evolution in γ / γ ′ superalloys, but its efficiency needs to be evaluated in γ / γ ′– γ ″– η / δ superalloys like INCONEL 706. Various heat treatments were tested using an in-house resistivimeter to study the precipitation and dissolution kinetic of η phase. Various isothermal treatments were tested and showed three different electrical resistivity evolutions depending on the temperature reflecting three different precipitation sequences: η phase only at high temperatures, γ ′/ γ ″ precipitation and transformation to η phase at intermediate temperatures, and γ ′/ γ ″ precipitation with no transformation to η phase at low temperature. Electrical resistivity proved to be efficient in monitoring the precipitation and dissolution kinetics in INCONEL 706 during various heat treatments and could be useful to determine time-temperature-transformation diagrams in γ / γ ′– γ ″– η / δ superalloys.
Finet et al. (Mon,) studied this question.