The microstructural evolution of a Ni-based superalloy under interrupted hot compressive deformation with different cooling rates in the inter-pass stage is investigated. It is found that metadynamic recrystallization (MDRX) in the inter-pass stage is more sensitive to the accumulated strain than the deformation temperature which is above the recrystallization temperature. The variations of both the grain distribution and the texture intensity caused by MDRX during the inter-pass stage result in variations of the yield stress (YS) and the work hardening (WH) rate in each stage. Results also show that the MDRX process in the inter-pass stage has a considerable influence on the final microstructure of three-pass compression. The final grain distribution is more uniform, and the compression texture gradually transforms into recrystallization texture with an increasing degree of MDRX. In order to predict the MDRX fraction in the inter-pass cooling stage, a modified kinetic equation is established, which can reasonably predict the MDRX behavior under multi-pass compression with different conditions in the inter-pass stage. Meanwhile, the influence of the inter-pass cooling stage on the mechanism of dynamic recrystallization (DRX) is studied. It is universally acknowledged that the discontinuous dynamic recrystallization (DDRX) process is the major deformation mechanism for the Ni-based superalloy. However, the continuous dynamic recrystallization (CDRX) process is promoted in the compression stage with a decrease of the cooling rate in each inter-pass stage.

The effect of pulsed current on tensile deformation of Inconel 718 superalloy with different initial microstructures was studied by experiment, which is of great importance for the subsequent application of electrically-assisted manufacturing (EAM) technology. The results show that the pulsed peak current with a density of 10 A/mm2 has no effect on stress responses, while the yield strength (YS) and ultimate tensile strength (UTS) are reduced when the peak current density is above 25 A/mm2. The higher peak current density and frequency lead to more obvious thermal effect and thus result in the decrease of YS, UTS and elongation. For samples cutting from different directions, i.e. transverse direction (TD) and rolling direction (RD), no difference in YS can be observed with EAM. For samples with different initial microstructures, e.g., the as-received and the heat-treated samples, more significant decrease in flow stress and higher elongation can be observed for the former than for the latter. Notably decreasing YS was achieved without deteriorating the ductility at a peak current density of 25A/mm2 and a frequency of 400Hz. The physical mechanism for the obtained rules was revealed.