Study and modelling in micro- and macro-structural scale of the phenomenon of re-crystallization in forged products in Ni-based superalloys

Hot forming is a fundamental technology to obtain good properties in any material, particularly for metallic alloys used in a variety of industrial fields, oil & gas, power generation, transport and aerospace applications. Mechanical properties of a forged component deeply depend on the grain size, and grain size depends on processing parameters, i.e. strain, strain rate and temperature. A key role in hot working is given by recrystallization, because it modifies microstructure along the process route and thus determines the final properties of products. In this work the phenomenon of dynamic recrystallization (DRX) has been studied on the commercial grade nickel-based superalloy Inconel 718 by means of compression testing and on actual forged components. Samples have been characterized with optical microscopy and by means of more advanced techniques, such as Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction, and electron back-scattered diffraction (EBSD) technique. Flow-stress curves obtained in the compression test have been analyzed to estimate the critical condition on which dynamic recrystallization begins, and process maps have been established; Zener-Hollomon (Z) parameter has been evaluated, as well as the apparent activation energy (Q) for DRX. EBSD maps were analyzed with the toolkit MTEX