INCONEL 718 Recrystallization in the Delta Supersolvus Domain

Abstract

An experimental study of compression tests at high temperature and different engineering strains was carried out on INCONEL 718 above the delta phase solvus. The objective is to investigate the mechanical behaviour in relation with the microstructure evolution. After deformation the samples were quenched with helium gas to avoid metadynamic recrystallization (MDRX). The quench efficiency is discussed by microstructural and hardness comparison. During forging process and without MDRX, there is generally a competition between deformation and dynamic recrystallization state (DRX) i.e. a dependence on dislocation density increase and dislocation annihilation, respectively. To investigate this competition, samples are characterized at different scales by EBSD method to determine local texture and grain size and by TEM to understand the dislocation evolution and determine the nucleation mechanism. In parallel, a numerical model using a three-dimensional finite element model of crystalline plasticity (CristalECP) has been developed in ABAQUS™ finite element code and coupled with a Recrystallization Cellular Automaton (CA_ReX). Results of forging process simulations are compared to those of experimental studies presented before and then discussed in terms of evolution.

INCONEL718 Single and Multipass Modelling of Hot Forging

“…A previous analysis proved that this transition starts from E ≈ 0.06 for a lower deformation rate on the same material. It has been shown that this transition corresponds to the nucleation of recrystallized grains [15]. This result will be used in the numerical part of this study.…”

“…It should be noted that the identification of the material parameters of the polycrystalline model were determined during the first deformation step, since it was previously proved that no dynamic recrystallization occurred for a deformation less than 0.06 [15]. Experimental and numerical stress-strain curves are given in Figure 9.…”

Role of δ-phase on recrystallisation behaviour of Inconel 718

“…However, with increased temperature, the δ-phase becomes unstable and dissolves in the matrix, and thus causes rapid grain-coarsening. 3,24 Some studies claim that the δ-phase dissolves in the matrix and diffuses into the voids and vacancies of grain boundaries before RX begins. However, a few studies concluded that the δ-phase precipitates along the grain boundaries as well as at shear bands following the nucleation of new grains.…”

“…However, a few studies concluded that the δ-phase precipitates along the grain boundaries as well as at shear bands following the nucleation of new grains. 3,15,24,25 Interestingly, some investigations that are focused on the fatigue, fracture, and creep behaviour of IN718, reported that the unique morphology of the δ-precipitates causes cracks to propagate in zigzag pattern both within the grains and along the grain boundaries, and thus help in improving the creep-fatigue life of the alloy. [26][27][28] From the above discussion, it is clear that the formation and the control of δ-phase play a crucial role in the processing and performance of IN718.…”

In Situ Characterization of Inconel 718 Post-Dynamic Recrystallization within a Scanning Electron Microscope

“…Dynamic and post-dynamic recrystallization is among the most important phenomena impacting the microstructure of hot-forged components. The influence of the thermomechanical forging conditions on dynamic recrystallization (DRX) kinetics and on the DRX grain size is relatively well established [1][2][3][4][5][6][7][8], and can even be predicted using either physical or empirical models [9][10][11][12][13][14][15]. However, previous studies have shown that post-dynamic evolutions may also considerably impact the final microstructure [12,[15][16][17][18].…”