Precipitation kinetics of niobium carbide (NbC) during homogenization heat treatment of additively manufactured inconel 718 superalloy

High cooling rate of the laser powder bed fusion (L-PBF) additive manufacturing can suppress the formation of niobium carbide (NbC) phase in the fabricated Inconel 718 nickel -based superalloy parts. However, it might precipitate during elevated temperature expo-sure. Accordingly, in the present work, the precipitation kinetics of the NbC carbide was investigated during homogenization heat treatment at temperatures in the range of 1000-1150 degrees C for soaking times of 15 min to 10 h. It was observed that increasing the homogenization temperature leads to the faster kinetics of NbC formation. The precipitation ki-netics was modeled by the general phase transformation kinetics formula (based on the transformed fraction of 0.5 or 50%, t0.5) and Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis, resulting in the precipitation activation energies of 159.2 and 157.4 kJ/mol, respectively. It was concluded that the diffusion of both C and Nb atoms in the Ni matrix are the underlying mechanisms for the NbC carbide formation during homogenization heat treatment. The relationship of 1/t0.5fexp(0.0097T) was also obtained for the precipitation rate as a function of temperature. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).