Microstructure evolution during dynamic recrystallisation in polycrystalline nickel superalloys

A new theory for describing grain structure evolution during discontinuous dynamic recrystallisation in nickel-based superalloys is presented. The evolution of the average and recrystallised grain size is determined during dynamic straining and at steady state by computing the variation in the number of grains with strain. The initial grain size distribution is combined with a size distribution function containing recrystallised grains only; subsequent evolution depends on their respective average values. This allows us to deconvolute the recrystallised and deformed grain distributions to obtain the recrystallised volume fraction. Precipitation pinning and solute drag are incorporated in the model by measuring the fractional loss of stored energy when a boundary encounters such defects depending on how they accumulate at the boundary. The model results are validated against data from eleven polycrystalline superalloys, covering a wide range in composition, initial microstructure and deformation regime.