Gamma Prime Precipitation in Cast and Wrought AD730® Superalloy

AD730®AD730® is a γ − γ′ polycrystalline superalloy which has been recently developed for future engine turbine discs. The γ′ precipitationPrecipitation influences mechanical propertiesMechanical properties at the service temperature but also the kinetics of recrystallizationRecrystallization during forgingForging process. Consequently, a deep understanding and monitoring of γ′ precipitationPrecipitation is required at each stage of the industrial process. The objective of this work is to understand the precipitationPrecipitation mechanism, determine the evolution of γ′ size during cooling and isothermal heat treatmentsHeat treatment, and calibrate a model for the nucleationNucleation and growth of γ′ during the ingot-to-billet conversionBillet conversion. The experimental analysis showed that water quenching at a cooling rate of 100 °C/s after a solution treatment at 1160 °C led to a fine and homogeneous γ′ precipitationPrecipitation for which the average circle radius ranges from 10 to 20 nm. Then, samples were heat treated between 1000 and 1080 °C with various holding times to characterize and quantify the size of precipitatesPrecipitates. The results were compared to the precipitationPrecipitation modeling using the in-house software PreciSo, a multi-class, Kampmann-Wagner Numerical precipitationPrecipitation model based on classical nucleationNucleation and growth theories. Even if the simulations of precipitationPrecipitation during isothermal heat treatmentsHeat treatment start with the correct initial radius, coarseningCoarsening appears to occur slower than predicted by the simulations. This discrepancy is attributed to one simulation parameter, the diffusivity of solute elements, which needs to be improved to obtain a better fit with experimentations.