Influence of Joule Effect Heating on Recrystallization Phenomena in Inconel 718

In this article, the Joule effect heating influence on recrystallization phenomena in the Inconel 718 nickel-based superalloy is investigated in details. On the one hand, static recrystallization kinetic studies at 1020 degrees C after cold deformation up to epsilon = 0.1 have been performed on a Gleeble 3800 machine, with Joule effect heating, and compared with conventional heating in a radiative furnace, reproducing exactly the same thermal paths in experiments. On the other hand, dynamic recrystallization kinetics have been compared between specimens deformed in the same conditions but varying the heating principle. Compression tests were thus performed on a MTS 250 (radiant heating) and on a Gleeble 3800 (Joule effect heating) at strain rates in the range (epsilon)over dot [10(-3); 1] s(-1) up to a macroscopic strain epsilon = 0.7 reproducing exactly the same thermomechanical paths. Compression tests were performed at two different nominal temperatures T = 1050 degrees C and 980 degrees C in order to investigate dynamic recrystallization in either delta-phase supersolvus or subsolvus conditions, respectively. As a general trend, Joule effect heating significantly accelerates recrystallization kinetics, and this holds for both static and dynamic recrystallization. Results also suggest that Joule effect heating significantly impacts other metallurgical phenomena like dislocations recovery mechanisms and delta-phase precipitation. The observed differences could not be totally explained by experimental biases resulting from Joule effect heating like radial temperature gradients or differences in initial microstructures. Interactions between electrons and microstructural features such as crystal defects, generally evoked in the literature, are indeed the most probable origin of Joule effect heating impact on microstructural evolutions. (C) The Minerals, Metals & Materials Society and ASM International 2021