Experimental and numerical investigations of the γ and γ′ precipitation kinetics in Alloy 718

Predictive simulations of the gamma' and gamma precipitates in the nickel-based superalloy Alloy 718 is needed for integrated computational materials engineering of technical components. But so far, no thermo-kinetic model is published for this alloy that is capable of reproducing simultaneously the precipitation evolution during, both, short and long time aging durations for an extended range of temperatures. The thenno-kinetic modeling was performed in the software package MatCalc, which uses the classical nucleation theory, the Svoboda-Fischer-Fratzl-Kozeschnik growth model and the 'generalized broken bond theory' for the interfacial energy. A combination of atom probe tomography, electron microscopy, small angle neutron scattering and sequential tensile tests are conducted to obtain the unknown kinetic evolution and strengthening parameters at the nano-, micro and macro-scales for the model. The role of the physical association of the gamma' and gamma precipitates and the effects of the precipitation strengthening are discussed. The resulting parametrized model successfully reproduces the measured local chemical composition, volume fractions, mean radii and precipitation strengthening contributions within a single set of model parameters up to 800 degrees C. Between 800 degrees C and 830 degrees C the model slightly over predicts the kinetics.