In Situ Small-Angle Neutron Scattering Study of Precipitation and Evolution Behavior of Secondary Phases in Ni-Based Superalloys
LI Yawei1, XIE Guang1(), KE Yubin2,3, LU Yuzhang1, HUANG Yaqi1, ZHANG Jian1()
1 Shi-changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 Spallation Neutron Source Science Center, Dongguan 523803, China 3 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
Cite this article:
LI Yawei, XIE Guang, KE Yubin, LU Yuzhang, HUANG Yaqi, ZHANG Jian. In Situ Small-Angle Neutron Scattering Study of Precipitation and Evolution Behavior of Secondary Phases in Ni-Based Superalloys. Acta Metall Sin, 2024, 60(8): 1100-1108.
The γ′ and γ′′ phases are crucial strengthening components in Ni-based superalloys. Understanding their precipitation and evolution mechanism during heat treatment is essential for tailoring the mechanical properties of the superalloys. Herein, GH4169 superalloy was used to investigate the precipitation and evolution behaviors of secondary phases during in situ standard heat treatment by time-of-flight small-angle neutron scattering. Further, transmission electron microscopy was employed to observe the secondary phases generated in samples after ex situ heat treatment. Results showed that the secondary phases, including the spherical γ′ phase and coprecipitates (mainly the γ′′/γ′/γ′′ sandwich structure), mostly occurred during the aging treatment. After the formation of coprecipitates during the first aging treatment (AT1), their quantity apparently remained stable during the second aging treatment (AT2). Furthermore, the average size of the γ′ phase and coprecipitates gradually increased during the AT1 stage while remaining almost constant during the AT2 stage. Throughout the aging process, the interface between spherical γ′ phase and γ matrix exhibited a decreased composition fluctuation, while the interface fluctuation of coprecipitates was always significant. Thus, it can be inferred that the precipitation and evolution behaviors of secondary phases are controlled by the element diffusion at the interface.
Fund: National Key Research and Development Program of China(2021YFA1600603);National Natural Science Foundation of China(52271042);National Natural Science Foundation of China(51911530154);National Natural Science Foundation of China(91860201);National Natural Science Foundation of China(U2141206);National Science and Technology Major Project(J2019-VI-0010-0124);CSNS Consortium on High-performance Materials of Chinese Academy of Sciences(JZHKYPT-2021-01);Science Center for Gas Turbine Project(P2022-C-IV-001-001)
Corresponding Authors:
XIE Guang, professor, Tel: (024)23971712, E-mail: gxie@imr.ac.cnZHANG Jian, professor, Tel: (024)23911196, E-mail: jianzhang@imr.ac.cn
Fig.1 In-situ heat treatment regime of GH4169 superalloy
Fig.2 Two-dimensional small-angle neutron scattering (SANS) patterns obtained during ST for 1 h (a), AT1 for 7 h (b), and AT2 for 7 h (c) (Qx —scattering vector along the x-axis, Qy —scattering vector along the y-axis, I—intensity)
Fig.3 One-dimensional SANS curves during ST (a), AT1 (b), and AT2 (c) for different time (Q—scattering vector mudulus, n1—Porod factor for low Q, n2—Porod factor for high Q)
Fig.4 Change of Porod factors during in situ aging treatment
Fig.5 Radius (R) evolution of disc-like second phases during in situ aging treatment
Fig.6 Size (r) distributions of sphere second phases during in situ AT1 (a) and AT2 (b)
Fig.7 Median radius (rmed) evolution of sphere second phases during in situ aging treatment
Fig.8 TEM images (a, c, e) and SAED patterns (b, d, f) of second phases in samples after ex situ treatment (a, b) ST state (c, d) ST + AT1 state (e, f) ST + AT1 + AT2 state
Fig.9 Schematic of disc-like sandwich structure for γ′′/γ′/γ′′ (R1—long axial radius, R2—short axial radius)
Sample state
Mean radius
nm
Shape factor
Number density
10-4 nm-2
Volume fraction
%
rγ′
R1(γ′′/γ′/γ′′)
R2 (γ′′/γ′/γ′′)
γ′′/γ′/γ′′
γ′
γ′′/γ′/γ′′
γ′
γ′′/γ′/γ′′
ST + AT1
11.2 ± 1.9
11.4 ± 3.6
7.3 ± 2.7
0.64
-
12.6 ± 0.6
-
30.8 ± 1.5
ST + AT1 + AT2
10.6 ± 4.7
14.4 ± 4.5
6.0 ± 1.3
0.42
-
12.5 ± 0.7
-
29.5 ± 1.0
Table 1 Quantitative summary of second phases in samples after ex situ treatment
Fig.10 Schematic of precipitation and evolution process for second phases (a) ST stage (b, c) AT1 stage (d, e) AT2 stage
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