Microstructural Evolution of Inconel 718 during Aging and Its Correlation with Electric Conductivity Measurements

The microstructural evolution of the nickel-base superalloy Inconel 718 after exposition at 750 degrees C for different holding times (10 min-1,000 h) was characterized and correlated with the Eddy current (EC) technique. The results showed that electrical conductivity increases with aging time. This behavior was associated with the precipitation and coarsening of the metastable gamma '' phase and its transformation into the detrimental delta phase after 100 h. EC nondestructive evaluation was correlated with X-ray diffraction patterns in terms of the precipitation and growth of secondary carbides that were observed in the scanning electron microscope. Vickers microhardness values were also in agreement with microstructural changes and EC measurements, as the maximum hardened condition can be associated with the precipitation of secondary phases before the transformation of the gamma '' phase into the delta phase.