Grain growth behaviour during near-γ′ solvus thermal exposures in a polycrystalline nickel-base superalloy Original Research Article

The grain growth behaviour that occurs during near solvus isothermal and transient heat treatments and the influence of primary γ′ has been studied in the advanced polycrystalline nickel-base superalloy, RR1000. Experimental observations showed that grain growth can be related to image, a theoretical grain size limit that accounts for the time dependent pinning contribution from the full primary γ′ precipitate size distribution. This term was also used to describe the pinning contribution from MC carbides, which limits grain size in the absence of primary γ′. The values of image were calculated using both experimental data and simulated data obtained from the software, PrecipiCalc. The Andersen–Grong grain growth model was modified to incorporate the pinning effect of primary γ′ and MC carbides. This was used to predict the grain sizes for a range of heat treatment times, incorporating the calculated image values. Material-dependent grain growth coefficients were simultaneously fitted by minimizing the difference between the simulated and experimental grain sizes. Good correlation was achieved between the modelled and experimental grain sizes, though agreement was superior with PrecipiCalc data. This was attributed to the removal of experimental scatter, found to be important when using this method.