Effects of Solution Post-Treatment on Precipitation Evolution During Aging of GH4706 Alloy and Its Mechanical Properties

doi:10.11900/0412.1961.2024.00090

Acta Metall Sin

2025, Vol. 61

Issue (11): 1638-1652 DOI: 10.11900/0412.1961.2024.00090

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Effects of Solution Post-Treatment on Precipitation Evolution During Aging of GH4706 Alloy and Its Mechanical Properties

WANG Chong¹, WANG Lei¹(

), DUAN Ran², TIAN Qiang², HUANG Shuo²(

), ZHAO Guangpu²

1 Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
2 Gaona Aero Material Co. Ltd., Beijing 100081, China

Cite this article:

WANG Chong, WANG Lei, DUAN Ran, TIAN Qiang, HUANG Shuo, ZHAO Guangpu. Effects of Solution Post-Treatment on Precipitation Evolution During Aging of GH4706 Alloy and Its Mechanical Properties. Acta Metall Sin, 2025, 61(11): 1638-1652.

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Abstract

GH4706 alloy is used for industrial gas turbine disks owing to its excellent properties, including high creep resistance, tensile strength, toughness, and microstructural stability up to approximately 650 ^oC. However, the increasing weight and size of large turbine disks have limited the cooling rate following the solution treatment, which hinders the control of the microstructure and mechanical properties of large GH4706 alloy disks. Herein, four solution post-treatments were conducted on a 1500-mm-diameter disk manufactured from GH4706 alloy after being treated at 980 ^oC for 4 h: air cooling + air cooling (AA), furnace cooling to 825 ^oC and stabilization treatment followed by air cooling (FSA), furnace cooling to 825 ^oC followed by air cooling (FA), and furnace cooling to 825 ^oC followed by asbestos cooling (FAs). The evolution of precipitates during aging (including for γ'/γ" coprecipitation and η phase) and their effects on mechanical properties were analyzed. Results indicated that reducing the cooling rate from 980 ^oC to 825 ^oC promoted the precipitation and growth of the η phase, leading to Ni and Ti consumptions. This inhibited γ'/γ" coprecipitation around the large η phase, thereby favoring the formation of a cellular microstructure. Further reduction in cooling rate from 825 ^oC to 600 ^oC substantially accelerated the growth of γ'/γ" coprecipitates into cubic forms. The volume fractions of the cellular microstructure in the FSA, FA, and FAs treatments were 4.1%, 1.0%, and 1.8%, respectively. The AA and FA treatments had negligible effects on the tensile properties of GH4706 alloy at room temperature; meanwhile, the FSA treatment slightly decreased tensile ductility. The FAs treatment led to a notable reduction in yield strength at room temperature. In impact testing at room temperature, the cellular microstructure accelerated crack initiation and propagation, resulting in a 64% lower impact toughness of GH4706 alloy for the FSA treatment compared to that for the AA treatment. However, during stress rupture testing at 650 ^oC, the cellular microstructure effectively hindered crack propagation and the growth and aggregation of micropores, thereby extending the rupture life. However, the FAs treatment reduced the rupture life due to strength loss caused by the large γ'/γ" coprecipitates. The FA treatment fostered an optimal level of cellular microstructure, thereby increasing the rupture life while maintaining excellent tensile and impact properties at room temperature, demonstrating remarkable overall mechanical properties.

Key words: GH4706 alloy cooling after solution treatment cellular microstructure impact toughness stress rupture property

Received: 24 March 2024

ZTFLH:

TG156.1

Fund: National Key Research and Development Program of China(2022YFB3705102)

Corresponding Authors: HUANG Shuo, senior engineer, Tel: (010)62188063, E-mail: shuang@cisri.com.cn

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	WANG Chong
	WANG Lei
	DUAN Ran
	TIAN Qiang
	HUANG Shuo
	ZHAO Guangpu

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https://www.ams.org.cn/EN/10.11900/0412.1961.2024.00090 OR https://www.ams.org.cn/EN/Y2025/V61/I11/1638

Fig.1 Schematic of sample cutting position in the GH4706 turbine disc (R—radius)

Fig.2 Schematics of solution post-treatment processes of GH4706 alloy
(a) air cooling + air cooling (AA) (b) furnace cooling + stabilization + air cooling (FSA)
(c) furnace cooling + air cooling (FA) (d) furnace cooling + asbestos cooling (FAs)

Fig.3 OM images (a, c, e, g) and EBSD grain boundary reconstruction maps (b, d, f, h) showing the grain microstructures of GH4706 alloy after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment (Arrows in Figs.3c, e, and g show the cellular microstructures, CSL—coincidence site lattice)

Table 1 Volume fractions of CSL boundaries in GH4706 alloy after different solution post-treatments and the two-stage aging treatment

Fig.4 Low (a, c, e, g) and locally high (b, d, f, h) magnified SEM images of γ'/γ" phase and η phase characteristics in GH4706 alloy after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment (PFZ—precipitation free zone)

Fig.5 TEM images and corresponding selected area electron diffraction (SAED) patterns (insets) of η phase (a, c, e, g) and γ'/γ'' phase (b, d, f, h) characteristics of GH4706 alloy after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment

Fig.6 High angle annular dark field (HAADF) image and corresponding EDS mappings of η phase in the cellular micro-structure

Fig.7 Transmission Kikuchi diffraction (TKD) image of geometrically necessary dislocation (GND) in cellular micro-structure (a) and corresponding normal distribution statistical diagram of GND density (b) (ρ_GND—GND density)

Table 2 Volume fractions of cellular microstructure and precipitation sizes and volume fractions of γ'/γ'' phase in GH4706 alloy after different solution post-treatments and the two-stage aging treatment

Fig.8 Comparisons of mechanical properties of GH4706 alloy after different solution post-treatments and the two-stage aging treatment
(a) tensile properties at room temperature (R_m—ultimate tensile strength, R_p0.2—yield strength, A—elongation, Z—reduction of area)
(b) impact toughness at room temperature
(c) stress rupture properties at 650 ^oC and 690 MPa (τ—stress rupture life, δ—elongation)

Fig.9 Fracture surface SEM images of impact samples after AA (a1-a3), FSA (b1-b3), FA (c1-c3), and FAs (d1-d3) solution post-treatments and the two-stage aging treatment with different magnifications (Red arrows in Figs.9a1-d1 denote the directions of cracks propagation, and yellow arrows in Figs.9c3 and d3 denote the intergranular fracture plane)

Fig.10 Low (a, c, e, g) and locally high (b, d, f, h) magnified fracture surface SEM images of stress rupture samples after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment (Yellow arrows in Figs.10d and f denote the step fracture features)

Fig.11 Continuous-cooling-transformation (CCT) diagrams of JMatPro simulation (a) and the actual solution post-treatments (b) (Inset in Fig.11b shows the locally enlarged diagram)

Fig.12 Kernel average misorientation (KAM) maps (a, c, e, g) and SEM images (b, d, f, h) showing the fracture morphologies of longitudinal sections of the impact test samples at room temperature after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment (Red arrows in Figs.12b, d, f, and h show the (Nb, Ti)C, and blue arrows in Figs.12d, f, and h show the cellular microstructures. Inset images in Figs.12d, f, and h show the locally enlarged views, inset curve in Fig.12d shows the EDS result of (Nb, Ti)C)

Fig.13 Impact load-displacement (a) and impact absorb energy-displacement (b) curves of GH4706 alloy after different solution post-treatments and the two-stage aging treatment (P_y—yield load, P_m—maximum load)

Table 3 Comparisons of the impact absorption energy components of GH4706 alloy after different solution post-treatments and the two-stage aging treatment

Fig.14 KAM maps (a, c, e, g) and SEM images (b, d, f, h) showing the fracture morphologies of longitudinal sections of the stress rupture test samples at 650 ^oC and 690 MPa after AA (a, b), FSA (c, d), FA (e, f), and FAs (g, h) solution post-treatments and the two-stage aging treatment (Blue arrows in Figs.14d, f, and h show the cellular microstructures. Inset images in Fig.14f show the locally enlarged views)

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