Hot Deformation Characteristics and Dynamic Recrystallization Mechanisms of a Novel Nickel‐Based Superalloy

Abstract

The hot deformation characteristics of a novel nickel‐based superalloy is investigated via the isothermal compression test in temperature range of 1000–1150 °C and strain rate of 0.001–10 s−1 under the true strain of 0.8. The hot deformation characteristics of GH4065 alloy are studied here for the first time. Based on the flow stress data, it is observed the typical features of flow curves exhibit the occurrence of dynamic recrystallization (DRX) during the hot deformation process. The constitutive equation in the Arrhenius‐type model is established, and activation energy (Q) is determined as 844.787 kJ mol−1. The microstructure evolution and DRX mechanism are investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) technique. The results reveal that the fraction of low angle grain boundaries (LAGBs) decrease gradually with the increase in deformation temperature, whereas the fraction of Σ3 boundaries increase first and then decrease. For γ + γ′ dual‐phase region, the particle‐induced DRX (PIDRX), characterized by the generation of sub‐grains accelerated by γ′ precipitates pinning dislocations, and discontinuous dynamic recrystallization (DDRX) are the dominant nucleation mechanism of DRX. For γ quasi‐phase region and γ single‐phase region, the occurrence of bulged grain boundaries with twins further illustrates that DDRX plays a more significant role.

Investigation on Sub-Solvus Recrystallization Mechanisms in an Advanced γ-γ’ Nickel-Based Superalloy GH4151

“…It suggested that the sub-grain merging and rotation becomes slight at the true strain of 0.5. This phenomenon demonstrates that the deformed grains transform into the dislocation-free DRX grains [28]. With the true strain further increasing from 0.5 to 0.7, it can be found that the point to origin misorientations obviously increases, and the point to point misorientations scarcely exceed 0.5 both along the G1 line and G2 line in Figure 4g, as shown in Figure 5g,h.…”

“…The similar evolution characteristic of the misorientation jumps is also shown in Figure 5a,b. This phenomenon indicates that different orientation bands exist in the deformed grains, resulting from different slip systems activated for coordinating the strain between the adjacent grains [28,36].With the true strain of 0.5, it is easily observed that the point to origin misorientations and the point to point misorientations obviously decreases, and scarcely exceed 0.3 • both along the E1 line and E2 line in Figure 4e, as shown in Figure 5e,f. It suggested that the sub-grain merging and rotation becomes slight at the true strain of 0.5.…”

“…This indicates that the interactions between Σ3 n boundaries are weaker. Therefore, it is concluded that the generation of Σ3 boundaries is attributed to the 'growth accident' mechanism [28].…”

“…Li et al [27] investigated the effect of different morphology and sizes of γ' phase on DRX of FGH4096 superalloy during the sub-solvus temperature range deformation, and concluded that coarse γ' particles can promote the occurrence of DRX behavior. Lv et al [28] observed that the occurrence of γ' particle-induced DRX (PIDRX) at the sub-solvus temperature of GH4065 alloy, deriving from the formation of sub-grains accelerated by γ', precipitates pinning dislocations.…”

Hot Deformation Behavior of a Powder Metallurgy Superalloy with High γ′ Content

“…[ 27 ] The dislocation density increased with strain until the critical strain point, and then, DRX was activated. [ 28 ] Finally, the flow stress was stable at a large strain, indicating that dynamic softening offset work hardening, leading to equilibrium. However, from the EP741NP alloy stress–strain curves, at low temperatures or high strain rates, dynamic equilibrium was not reached even at a maximum strain of 0.5, and this was mainly ascribed to incomplete DRX.…”