Creep Behavior of a Ni-Based Superalloy with Strengthening of γ' and γ'' Phases
ZHOU Shengyu1, HU Minghao1, LI Chong1(), DING Haimin2, GUO Qianying1, LIU Yongchang1
1 School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China 2 Hebei Key Laboratory of Electric Machinery Health Maintenance and Failure Prevention, North China Electric Power University, Baoding 071003, China
Cite this article:
ZHOU Shengyu, HU Minghao, LI Chong, DING Haimin, GUO Qianying, LIU Yongchang. Creep Behavior of a Ni-Based Superalloy with Strengthening of γ' and γ'' Phases. Acta Metall Sin, 2025, 61(2): 226-234.
Ni-based superalloys have shown great application potential as component materials in aircraft engines because of their excellent mechanical properties at high temperatures. With the development of engine and power plant boiler tubes, the high-temperature creep resistance of nickel-based superalloys has become an important indicator for evaluating the mechanical properties of superalloys. In this study, the creep behavior of the as-cast Ni-based superalloy with the coprecipitation of γ′ and γ″ phases at 750 oC and 120 MPa was investigated. The results show that the creep deformation behavior and creep property change with the size of the γ'/γ'' phases. A number of dislocations are cut into the γ'/γ'' phases, forming continuous stacking faults in the γ channel and γ'/γ'' phases when a high amount of compact γ'/γ'' phases are precipitated, leading a inferior creep property. Increasing the size of the γ'/γ'' phases, the dislocations are easily cut in the γ′ phase and isolated stacking faults are formed in the γ′ phase, which significantly enhances the creep property. Further increasing the size of the γ′ phase, the dislocations are piled up on the interface of the γ/γ′ phases, and the γ′ phase is looped with dislocations, which decreases the creep property. Given the precipitation of the deleterious Laves phases, the grain boundaries (GBs) are weakened. However, the stretch of cracks is restrained, and the creep properties of the alloy are enhanced because of the moderate needle-like η/δ phases in the GBs. The precipitation of the overdose η/δ phases provides a favorable location for crack nucleation and accelerates alloy failure.
Fund: National Natural Science Foundation of China(52122409);Hebei Key Laboratory of Electric Machinery Health Maintenance & Failure Prevention Fund(KF2021-03);Tianjin Natural Science Foundation(20JCYBJC00950)
Corresponding Authors:
LI Chong, professor, Tel: 13021398676, E-mail: lichongme@tju.edu.cn
Fig.1 SEM images of as-cast Ni-based superalloy (a) interdendritic region (b) γ′/γ″ phases
Fig.2 SEM images (a, d, g) and TEM images with different magnifications (b, c, e, f, h, i) of Ni-based superalloy after heat treatment (GB—grain boundary) (a-c) HDA-7 (d-f) HDA-8 (g-i) HDA-9
Fig.3 High-temperature creep curves (750 oC, 120 MPa) of Ni-based superalloy specimens after different heat treatments (a) creep time-strain curves (b) creep time-strain rate curves
Specimen
Creep life / h
Creep strain / %
Steady creep rate / h-1
HDA-7
257.6
0.2
1.1 × 10-5
HDA-8
1898.6
0.7
4.9 × 10-7
HDA-9
1793.5
1.5
2.2 × 10-6
Table 1 High-temperature creep properties for different specimens
Fig.4 TEM images of γ'/γ'' phases of HDA-7 (a), HDA-8 (b), and HDA-9 (c) specimens after crept, and the average sizes of γ' (d) and γ'' (e) phases
Fig.5 TEM images of microstructures of HDA-7 (a-c), HDA-8 (d, e), and HDA-9 (f, g) specimens after creep (SFs—stacking faults)
Fig.6 SEM images of creep fracture surfaces of HDA-7 (a-c), HDA-8 (d-f), and HDA-9 (g-i) specimens with different magnifications
Fig.7 EBSD-KAM maps of HDA-7 (a), HDA-8 (b), and HDA-9 (c) specimens (KAM—kernel average misorientation, σ—creep stress)
Fig.8 SEM images of longitudinal sections near the fractures of HDA-7 (a), HDA-8 (b), and HDA-9 (c)
Fig.9 Schematics of microstructure evolution, crack propagation, and deformation mechanism before (a-c) and after (d-f) creep (a, d) HDA-7 (b, e) HDA-8 (c, f) HDA-9
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