Microstructure Evolution and Mechanical Properties of a Novel Low-Cost Second-Generation Ni-Based Single Crystal Superalloy After Long-Term Thermal Exposure

doi:10.1007/s40195-025-01923-0

Abstract

Abstract:

This study investigates the microstructural evolution of a novel low-cost second-generation Ni-based single crystal superalloy during long-term thermal exposure at different temperatures (982 °C, 1038 °C, 1093 °C) and its impact on the stress rupture properties of alloy. The results reveal that the γ′ phase undergoes coarsening and rafting at high temperatures, and its growth behavior follows the Ostwald ripening mechanism. With the increase in aging temperature and extension of aging time, the coarsening rate of the γ′ phase increases significantly. Particularly at 1093 °C, the γ′ phase undergoes the most pronounced growth, leading to a remarkable deterioration of its precipitation strengthening effect. Furthermore, under conditions of higher temperature and longer time, minor amounts of topologically close-packed (TCP) phase precipitate. As the aging temperature rises and time elapses, the precipitation tendency of the TCP phase shows a slight increase. The stress rupture testing at 1100 °C/120 MPa demonstrates that the stress rupture life decreases significantly with the increase in thermal exposure temperature and time. This is mainly attributed to the diminished precipitation strengthening effect of the γ′ phase and the deteriorating effect of the TCP phase. However, under the same conditions, the stress rupture properties of this alloy are comparable to those of the DD5 alloy. This research provides theoretical support for enhancing the service stability and reliability of single crystal turbine blades, and offers a reference for the development of cost-effective and high-performance turbine blade materials.

Key words: Ni-based superalloys, Thermal exposure, Microstructure, Stress rupture properties

Chongwei Zhu, Zhipeng Zhang, Jide Liu, Jinchao Ma, Jiajian Wang, Wenying Zhang, Xinguang Wang, Yizhou Zhou, Jinguo Li. Microstructure Evolution and Mechanical Properties of a Novel Low-Cost Second-Generation Ni-Based Single Crystal Superalloy After Long-Term Thermal Exposure[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(11): 2035-2046.

Figures/Tables 13

Table 1 Chemical composition of the experimental alloy (wt%)

W	Ta	Al	Cr+Co+Mo	Re	Hf	Ni
6-6.5	6.3-6.7	6-6.5	14-16	1.3-1.7	0.5-0.7	Bal.

Fig. 1 Schematic diagram of the stress rupture sample (unit: mm)

Fig. 2 SEM images under different treatments of the alloy: a solution treatment, b the CHT

Fig. 3 Microstructures of samples after different thermal exposures: a-c at 982 °C for 200 h, 600 h, 1000 h, d-f at 1038 °C for 200 h, 600 h, 1000 h, g-i at 1093 °C for 200 h, 600 h, 1000 h

Fig. 4 Statistical analysis of γ′ phase in alloys after different thermal exposures: a average size, b area fraction, c coarsening kinetics

Fig. 5 TCP phase evolution in samples after different thermal exposure: a-c at 982 °C for 200 h, 600 h, 1000 h, d-f at 1038 °C for 200 h, 600 h, 1000 h, g-i at 1093 °C for 200 h, 600 h, 1000 h

Table 2 TCP phase area fraction after different thermal exposure (%)

Temperature (°C)	Time (h)
Temperature (°C)	200	600	1000
1038	/	0.001552	0.001893
1093	0.002438	0.003325	0.004051

Table 3 Chemical composition of TCP phase after prolonged exposure at 1038 °C for different time (at.%)

Time (h)	Al	Cr	Co	Ni	Mo	Hf	Ta	W	Re
600	0.98	7.63	6.05	17.37	15.85	0.72	7.09	37.73	6.57
1000	0.38	8.03	5.97	15.19	17.31	0.47	7.11	38.81	6.74

Table 4 Chemical composition of TCP phase after prolonged exposure at 1093 °C for different time (at.%)

Time (h)	Al	Cr	Co	Ni	Mo	Hf	Ta	W	Re
200	0.76	6.7	4.98	16.49	14.75	0.62	8.5	40.49	6.72
600	0.45	6.66	5.22	15.07	14.34	0.46	8.76	42.12	6.92
1000	0.77	6.85	5.28	17.25	13.43	0.53	8.55	40.55	6.79

Fig. 6 Stress rupture properties of samples at 1100 °C/120 MPa after different thermal exposures: a stress rupture life, b elongation

Fig. 7 The γ/γ′ microstructures of samples after 1000 h thermal exposure at different temperatures, followed by stress rupture testing at 1100 °C/120 MPa: a 983 °C, b 1038 °C, c 1093 °C

Fig. 8 Fracture morphologies in samples at different thermal exposure temperatures for 1000 h after stress rupture at 1100 °C/120 MPa: a, d, g 983 °C; b, e, h 1038 °C; c, f, i 1093 °C

Fig. 9 High-angle annular dark-field (HAADF) images and corresponding elemental mappings of TCP phase in the alloy after prolonged thermal exposure at 1093 °C for 1000 h

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