Comparison of the phase compositions in Alloy 718 measured by atom probe tomography and predicted by thermodynamic calculations

A comparison has been made of the phase compositions predicted by thermodynamic calculations and measured by atom probe tomography in a commercial Alloy 718 nickel based superalloy. The results indicate that caution should be taken in the application of the NiFe database/Thermocalc™ to superalloys because some of the predicted phases may not correspond to actual microstructure of commercial alloys. When microstructural information is taken into account and absent phases are suppressed in the calculations, reasonable agreement between the atom probe data and the thermodynamic predictions may be achieved.