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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.

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Nickel-based superalloys are widely applied in aeronautical, aerospace, nuclear, and petrochemical industries, due to their excellent high-temperature mechanical properties. [1-3] Disc superalloys, such as Allvac 718Plus, [4] Waspaloy, [5] FGH100L, [6] and GH4065, [7,8] are the typical representatives of nickel-based superalloys for the critical rotating components of aircraft engines and gas turbines. The nickel-based alloy GH4065 developed for aerospace turbine disc superalloys is strengthened by gamma prime (γ 0) precipitates (L1 2 structure, Ni 3 (Al, Ti)). Also, GH4065 was designed as a novel disc superalloy for service temperature up to 750 C. For turbine discs, it is usually formed by hot die forging. The microstructure of GH4065 alloy after forging is generally not uniform due to inhomogeneous plastic deformation, which is inevitable and cannot be ignored in the forging process. [9] Generally, the properties of components largely rely on their microstructure, and a homogeneous microstructure is essential to achieve better performance. Consequently, it is necessary to pay attention to the relationship among processing variables, microstructure, and properties for disc superalloys. Heat treatment plays a significant role in controlling the microstructure and properties for disc superalloys. Traditionally, heat treatment combined with solution treatment and aging treatment is adopted to adjust the microstructure and performance of nickel-based superalloys. For the conventional heat treatment, previous studies reported the influence of heat treatment on microstructural evolution or mechanical properties of nickel-based superalloys. [9-20] Jackson and Reed [10] pointed out that the heat treatment of 24 h at 700 C is the optimal condition for the creep properties of a disc superalloy, Udimet 720Li. In these studies, particular attention is only paid to the characterization of γ 0 particle size distributions. Chang et al. [16] showed that the direct aging heat treatment is the best one for the hot-isostatic-pressed Inconel 718 powder compact, due to the balance of strength and ductility. However, its yield strength (YS) is lower than that of the one that is solution treated because of the aging of precipitates. Chen et al. [9] proposed the optimum annealing parameters are 980 C for 10 min, which lead to the occurrence of static recrystallization (SRX) and improve the homogeneous nature of GH4169 alloy. However, the effect of preannealing (PA) prior to solution treatment on the evolution of strengthened phase, mechanical properties, and deformation mechanism is not discussed in the aforementioned studies. Moreover, the effect of PA on both microstructural evolution and tensile properties in disc superalloys has been barely reported till now. The PA in other alloys was studied, such as dual-phase steels, [21] stainless steel fiber felt, [22] and corrosion-resistant superalloy.

The superplastic deformation of a hot-extruded GH4151 billet was investigated by means of tensile tests with the strain rates of 10−4 s−1, 5 × 10−4 s−1 and 10−3 s−1 and at temperatures at 1060 °C, 1080 °C and 1100 °C. The superplastic deformation of the GH4151 alloy was reported here for the first time. The results reveal that the uniform fine-grained GH4151 alloy exhibited an excellent superplasticity and high strain rate sensitivity (exceeded 0.5) under all experimental conditions. It was found that the increase of strain rate resulted in an increased average activation energy for superplastic deformation. A maximum elongation of 760.4% was determined at a temperature of 1080 °C and strain rate of 10−3 s−1. The average activation energy under different conditions suggested that the superplastic deformation with 1 × 10−4 s−1 in this experiment is mainly deemed as the grain boundary sliding controlled by grain boundary diffusion. However, with a higher stain rate of 5 × 10−4 s−1 and 1 × 10−3 s−1, the superplastic deformation is considered to be grain boundary sliding controlled by lattice diffusion. Based on the systematically microstructural examination using optical microscope (OM), SEM, electron backscatter diffraction (EBSD) and TEM techniques, the failure and dynamic recrystallization (DRX) nucleation mechanisms were proposed. The dominant nucleation mechanism of dynamic recrystallization (DRX) is the bulging of original grain boundaries, which is the typical feature of discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) is merely an assistant mechanism of DRX. The main contributions of DRX on superplasticity elongation were derived from its grain refinement process.