Discontinuous Dynamic Recrystallization of Inconel 718 Superalloy During the Superplastic Deformation

Abstract

The superplastic behavior of Inconel 718 superalloy with particular emphasis on the microstructural evolution has been systematically investigated through tensile tests at the strain rate of 10 À3 s À1 and the temperatures ranging from 1223 K to 1253 K (950°C to 980°C). Its elongations exceeded 300 pct under all of the experimental conditions and peaked a maximum value of 520 pct at 1223 K (950°C). Moreover, the stress reached the top value at the strain of 0.3, and then declined until the tensile failure. In addition, we have found that the grain size reduced after deformation while the d phase precipitation increased. Microstructural evolution during the superplasticity was characterized via transmission electron microscope, and the randomly distributed dislocation, dislocation network, dislocation arrays, low-angled subgrains, and high-angled recrystallized new grains were observed in sequence. These new grains were found to nucleate at the triple junction, twin boundary, and near the d phase. Based on these results, it is deemed that the discontinuous dynamic recrystallization occurred as the main mechanism for the superplastic deformation of Inconel 718 alloy.

EBSD Study of Delta-Processed Ni-Based Superalloy

“…The structural parameters needed to identify the δ-phase (Ni3Nb) by EBSD are presented in Table 2. In accordance with the literature [36,37], Ni3Nb is an ordered and orthorhombic phase, having the space group Pmmn n°59, and the following lattice constants: a = 5.114 Å, b = 4.244 Å, and c = 4.538 Å. It is a center symmetric structure with eight atoms per unit cell, and because cell parameters b and c are similar, this phase can be considered distorted tetragonal.…”

“…The fraction of LAGBs has been also investigated, and the results indicate that it decreases with the increase of the deformation temperature. Additionally, the decrease of the strain rate and the small fraction of LAGBs indicate that continuous dynamic recrystallization (CDRX) plays a minor role in the nucleation of dynamic recrystallization in nickel-based superalloy, at least at relatively high temperatures and low strain rates [36]. The microstructural evolution during superplastic deformation of Inconel 718 and the grain size after deformation, while the δ-phase precipitation is increased, have been also studied.…”

A Combined Method to Model Dynamic Recrystallization Based on Cellular Automaton and a Phenomenological (CAP) Approach

“…It can be observed that original grains are compressed and elongated so as to be perpendicular to the compression axis, while the recrystallized area consists of equiaxed grains. It is clear that DRX grains are not distributed just along the initial grain boundaries, because according to the experimental reports [56,57] it is concluded that CDRX is the dominant softening process of the TiNiFe alloy through the high-temperature deformation. The most important limitation of the proposed model is its inability to take into account the inhomogeneity of deformation.…”

Superplastic Deformation and Dynamic Recrystallization of a Novel Disc Superalloy GH4151

“…The growth of grain was observed after 980 °C, because the dissolution of δ phase at high temperature decreased the resistance of the migration of the grain boundary [24]. Huang et al [25] studied the microstructural evolution of Inconel 718 alloy during the superplasticity and concluded that the discontinuous dynamic recrystallization (DDRX) is the main deformation mechanism for the superplasticity. Huang and Blackwell [26] carried out the optimum deformation condition for IN718 sheet at 965 °C with a strain rate of 10 −4 s −1 and observed the grain size reduction.…”