Hot deformation behaviour, constitutive model description, and processing map analysis of superalloys: An overview of nascent developments

This review article provides an in-depth discussion on the hot deformability, processing map analysis, and microstructural development in superalloys, as well as the associated constitutive equations employed in flow stress prediction. It describes how hot working can improve the grain structure of superalloys by dynamic recrystallization (DRX), reduce defects, and enhance their mechanical characteristics. The formation of necklace structures, work-hardening analysis to identify the existence and commencement of dynamically recrystallized grains and the influence of processing conditions on DRX grain size are all addressed in this article. The influence of deformation variables, described by the Zener-Hollomon parameter - the occurrence of phases, dynamic precipitation, and alloying elements on the thermomechanical response, and the restoration processes of DRV and DRX are discussed in detail. The utilization of processing maps as a means to determine the most favourable processing conditions and identify the instability regime, encompassing flow instability, defects and cracking, that may arise during the hot-working of superalloys are discussed. Specifically concerning the constitutive modelling of flow stress for characterizing material flow (at various deformation strain rates, temperatures, and strain), the application of threshold stress (as a result of phase transformation during hot deformation), temperature-dependent Young's modulus, and comparing the experimentally observed activation energy and deformation stress exponent to the values predicted by creep theories, are discussed. Also, an analysis of the various modelling techniques and equations for predicting flow curves during hot-working processing is evaluated. Finally, some recommendations are made regarding the potential future research directions.