Effect of Preannealing on Microstructural Evolution and Tensile Properties of a Novel Nickel‐Based Superalloy

Abstract

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.

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

“…To meet the need of turbine disks in the next-generation engine, several novel superalloys have been developed in previous studies, such as Allvac 718Plus, [7] Udimet 720Li, [8,9] AD730, [10] FGH100L, [11] GH4151, [12] and GH4065. [13,14] GH4065 alloy, a novel cast and wrought (C and W) superalloy, was developed as a highly alloyed γ-γ 0 nickel-based superalloy used for turbine disks superalloy at a service temperature up to 750 C. Due to its excellent high-temperature performance, GH4065 is widely applied to hot components of aeroengines. The alloy has been one of the optimized materials for critical rotating components, such as turbine disks and blades, in the range of 700-750 C for high-performance aeroengines.…”

“…To meet the need of turbine disks in the next‐generation engine, several novel superalloys have been developed in previous studies, such as Allvac 718Plus, [ 7 ] Udimet 720Li, [ 8,9 ] AD730, [ 10 ] FGH100L, [ 11 ] GH4151, [ 12 ] and GH4065. [ 13,14 ]…”

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

“…However, next generation engines are increasingly demanding, and a higher temperature capacity of turbine disks is required in order to improve the engine performance. Traditionally used alloys, such as Inconel 718 (limited to 650 °C) [ 3 ], 718Plus (limited to 710 °C) [ 4 ], Udimet 720Li (limited to 730 °C) [ 5 , 6 ], GH4065 [ 7 ], and AD730 (limited to 750 °C) [ 8 ] are already pushed towards their limits in view of the stability of the microstructure and mechanical properties, resulting in the development of an advanced nickel-based superalloy.…”

Creep Behaviors and Deformation Mechanisms at Intermediate Temperatures in a Novel γ‐γ′ Nickel‐Based Superalloy

“…To achieve this objective, next-generation polycrystalline γ-γ 0 nickel-based superalloys are newly developed for turbine disks at service temperatures up to 750 °C. [6,7] Especially for the newly developed disk superalloys, it is essential to have a better understanding of creep deformation mechanisms under their service conditions.Generally, the creep performance depends on deformation parameters, such as temperature, stress, strain, and microstructure, which have been investigated by several groups. Viswanathan et al [9] studied that creep deformation mechanisms at 650 °C/(790-972 MPa) in René 88DT and demonstrated that the transition of creep mechanism from micro-twinning to shearing by 1/2[110] dislocations and Orowan looping around the larger secondary precipitates when lower applied stress change to higher applied stress.…”

“…To achieve this objective, next-generation polycrystalline γ-γ 0 nickel-based superalloys are newly developed for turbine disks at service temperatures up to 750 °C. [6,7] Especially for the newly developed disk superalloys, it is essential to have a better understanding of creep deformation mechanisms under their service conditions.…”