Grain growth and particle pinning in a model Ni-based superalloy

An experimental study has been performed on the grain growth in a model Ni-based superalloy, with particular emphasis on the pinning effect of the second-phase particles. Extensive annealing experiments were performed, and the microstructural development was evaluated in detail using scanning and transmission electron microscopy. It was found that grain growth was strongly inhibited by the pinning effect of both the coarse γ′ phase and the inert precipitates. For samples heat-treated at temperatures below the γ′ solvus (1143 °C), the limiting grain size was determined by the size and volume fraction of the γ′ phase. For samples heat-treated at super-solvus temperatures, the stability of the MC-type carbides and yttrium oxides led to a nearly constant Zener limiting grain size over the temperature range 1143-1244 °C. Samples heat-treated at 1270 °C had larger grain sizes due to the coarsening and/or dissolution of the MC-type carbides and yttrium oxides.