1School of Materials Science and Engineering, Xi'an University of Technology, Xi'an 710048, China 2Science and Technology on Advanced High Temperature Structural Materials Laboratory, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China
Cite this article:
ZHANG Leilei, CHEN Jingyang, TANG Xin, XIAO Chengbo, ZHANG Mingjun, YANG Qing. Evolution of Microstructures and Mechanical Properties of K439B Superalloy During Long-Term Aging at 800oC. Acta Metall Sin, 2023, 59(9): 1253-1264.
The K439B alloy is a novel equiaxed superalloy and is used for producing hot section components that need to resist high temperatures in aero engines and gas turbines as its temperature capacity exceeds 800oC. In this study, the evolution of the microstructure and mechanical properties of K439B equiaxed superalloy after being subjected to long-term aging at 800oC for 3000 h was examined. The predominant deformation mechanisms affecting room-temperature tensile and stress rupture properties at 815oC and under 379 MPa stress following different aging durations for the K439B alloy were investigated.Results indicate that for heat-treated alloy, the morphology of the γ' phase is spherical, MC carbide is generated in the interdendritic region and grain boundaries, while M23C6 carbide is in the grain boundaries. During long-term aging at 800oC, γ′ precipitates conform to the Ostwald ripening mechanism for growth and tend to take a cubic form; the coarsening rate of the γ′ phase is calculated to be 71.7 nm3/h; Additionally, the MC carbide deteriorates while the content of M23C6 carbide gradually increases. After long-term aging for 3000 h, the precipitated grain boundary phase comprises MC carbide, γ′ phase, and M23C6 carbide; the orientation relationship between γ′ phase and M23C6 carbide can be described as [111] γ' //[111] MC and () γ′ //() MC. The heat-treated alloy demonstrates room-temperature tensile and yield str-engths of 1159.0 MPa and 911.5 MPa, respectively. Meanwhile, the stress rupture life at 815oC and under 379 MPa stress is 150.4 h. As the size of γ′ precipitates increases, the dominant deformation mechanism shifts from dislocation slipping in the matrix to dislocation cutting through the γ′ phase after long-term aging, resulting in superior stacking faults appeared in the γ′ phase. Consequently, the room-temperature tensile strength and stress rupture life show reduction at 815oC and under 379 MPa stress.
Fund: National Science and Technology Major Project of China(J2019-VI-0004-0117);National Key Research and Development Program of China(2022YFB3706804);Science and Technology on Advanced High Temperature Structural Materials Laboratory Fund(6142903210104);Science and Technology on Advanced High Temperature Structural Materials Laboratory Fund(6142903220101);AECC Science and Technology Innovation Platform Project(CXPT-2018-006)
Fig.1 Low (a, c, e) and high (b, d, f) magnified OM images of microstructures of K439B alloy subjected to long-term aging at 800oC for 0 h (a, b), 1000 h (c, d), 3000 h (e, f) (GB—grain boundary)
Fig.2 Typical microstructures of γ′ precipitates in the dendrite core of K439B alloy subjected to long-term aging at 800oC for 0 h (a), 100 h (b), 500 h (c), 1000 h (d), 2000 h (e), and 3000 h (f)
Fig.3 Size distributions of γ′ precipitates in the dendrite core of K439B alloy subjected to long-term aging at 800oC for 0 h (a), 100 h (b), 500 h (c), 1000 h (d), 2000 h (e), and 3000 h (f)
Aging
Average
Volume
Feret ratio
time / h
size / nm
fraction / %
0
47.0 ± 1.9
22.9 ± 1.2
1.09 ± 0.03
100
51.8 ± 1.4
23.4 ± 0.9
1.29 ± 0.02
500
74.3 ± 2.3
23.7 ± 1.0
1.34 ± 0.01
1000
92.4 ± 2.5
23.1 ± 0.8
1.36 ± 0.01
2000
112.6 ± 3.5
23.2 ± 1.6
1.39 ± 0.01
3000
120.3 ± 2.2
24.5 ± 1.7
1.42 ± 0.01
Table 1 Size, volume fraction, and shape factor of γ′ precipitates in the dendrite core of K439B alloy subjected to long-term aging at 800oC
Fig.4 Relationship between size of γ′ precipitates in the dendrite core and aging time of K439B alloy at 800oC (—average radius of γ′ after aging for 0 h; —average radius of γ′ after aging for time t; k—LSW theory coarsening rate constant; R2—coefficient of determination)
Fig.5 Evolution of carbide distributed in the interdendritic region (a, c, e) and at the grain boundary (b, d, f) of K439B alloy subjected to long-term aging at 800oC for 0 h (a, b), 1000 h (c, d), and 3000 h (e, f)
Fig.6 Carbide in the heat-treated K439B alloy (a) MC carbide distributed in the interdendritic region (b) HRTEM image from the edge of the MC carbide (marked with an arrow in Fig.6a) and the atomic-scale HRTEM images from the regions 1# and 2# with corresponding fast Fourier transform (FFT) patterns (insets) (c, d) MC carbide (c) and M23C6 carbide (d) at the grain boundary with corresponding SAED patterns (insets)
Fig.7 Grain boundary precipitated phase, SAED patterns of regions 1#-3#, and EDS compositional mapping of K439B alloy subjected to long-term aging at 800oC for 3000 h
Aging time
Interdendritic region
Grain boundary
h
%
%
0
-
20.86
100
-
23.64
500
-
25.98
1000
2.34
29.40
2000
6.58
36.43
3000
10.19
38.93
Table 2 Contents of M23C6 carbide in the interdendritic region and at grain boundary of K439B alloy subjected to long-term aging at 800oC
Fig.8 Room temperature tensile properties (a) and 815oC, 379 MPa stress rupture properties (b) of K439B alloy subjected to long-term aging at 800oC (σb—tensile strength, σp0.2—yield strength, δ—elongation, τ—stress rupture life )
Fig.9 Dislocation structures near room temperature tensile fracture surface of K439B alloy subjected to long-term aging at 800oC for 0 h (a, b), 1000 h (c, d), and 3000 h (e, f)
Fig.10 Dislocation structures near 815oC, 379 MPa stress rupture fracture surface of K439B alloy subjected to long-term aging at 800oC for 0 h (a-c) and 3000 h (d-f)
Fig.11 Schematics of microstructural evolution of K439B alloy during long-term aging at 800oC for 0 h (a), 1000 h (b), and 3000 h (c) (ID—interdendritic region)
1
Guo J T. Materials Science and Engineering for Superalloys [M]. Beijing: Science Press, 2008: 4
郭建亭. 高温合金材料学-上册-应用基础理论 [M]. 北京: 科学出版社, 2008: 4
2
Detrois M. Advancing development and application of superalloys [J]. JOM, 2020, 72: 1783
doi: 10.1007/s11837-020-04124-5
3
Schwant R, Shen C, Soare M. New materials enable unprecedented improvement in turbine performance [J]. Adv. Mater. Process., 2013, 171(1): 18
4
Sun B D, Wang J, Shu D. Precision Forming Technology of Large Superalloy Castings for Aircraft Engine [M]. Shanghai: Shanghai Jiao Tong University Press, 2016: 1
Anderson M, Thielin A L, Bridier F, et al. δ Phase precipitation in Inconel 718 and associated mechanical properties [J]. Mater. Sci. Eng., 2017, A679: 48
7
Anbarasan N, Gupta B K, Prakash S, et al. Effect of heat treatment on the microstructure and mechanical properties of Inconel 718 [J]. Mater. Today Proc., 2018, 5: 7716
8
Chen J Y, Ren X D, Zhang M J, et al. Microstructure and typical properties of cast Ni-based superalloy K439B [J]. Heat Treat. Met., 2023, 48(1): 100
doi: 10.13251/j.issn.0254-6051.2023.01.017
Zhang P, Yuan Y, Yan J B, et al. Morphological evolution of γ' precipitates in superalloy M4706 during thermal aging [J]. Mater. Lett., 2018, 211: 107
doi: 10.1016/j.matlet.2017.09.096
10
Guo X T, Zheng W W, An W R, et al. High temperature creep behavior of a cast polycrystalline nickel-based superalloy K465 under thermal cycling conditions [J]. Materialia, 2020, 14: 100913
doi: 10.1016/j.mtla.2020.100913
11
Kang M D, Sridar S, Xiong W. Influence of long-term aging on microstructural stability and performance of DD6 superalloy [J]. Mater. Sci. Technol., 2021, 37: 607
doi: 10.1080/02670836.2021.1938837
12
Wu R H, Yin Q, Wang J P, et al. Effect of Re on mechanical properties of single crystal Ni-based superalloys: Insights from first-principle and molecular dynamics [J]. J. Alloys Compd., 2021, 862: 158643
doi: 10.1016/j.jallcom.2021.158643
13
Jahangiri M R, Abedini M. Effect of long time service exposure on microstructure and mechanical properties of gas turbine vanes made of IN939 alloy [J]. Mater. Des., 2014, 64: 588
doi: 10.1016/j.matdes.2014.08.035
14
Jahangiri M R, Arabi H, Boutorabi S M A, et al. Comparison of microstructural stability of IN939 superalloy with two different manufacturing routes during long-time aging [J]. Trans. Nonferrous Met. Soc. China, 2014, 24: 1717
doi: 10.1016/S1003-6326(14)63245-3
15
Ou M Q, Ma Y C, Hou K L, et al. Effect of grain boundary precipitates on the stress rupture properties of K4750 alloy after long-term aging at 750oC for 8000 h [J]. J. Mater. Sci. Technol., 2021, 92: 11
doi: 10.1016/j.jmst.2021.03.022
16
Ou M Q. Strengthening mechanism of K4750 alloy for the large skew plate bearing frame application [D]. Hefei: University of Science and Technology of China, 2018
Liu G, Xiao X S, Véron M, et al. The nucleation and growth of η phase in nickel-based superalloy during long-term thermal exposure [J]. Acta Mater., 2020, 185: 493
doi: 10.1016/j.actamat.2019.12.038
18
Cui J Y, Zhang J T, Yao J. Effect of thermal exposure on the microstructure and stress-rupture properties of a directionally solidified superalloy [J]. J. Mater. Eng. Perform., 2021, 30: 9200
doi: 10.1007/s11665-021-06124-1
19
Chen J B, Huo Q Y, Chen J Y, et al. Tailoring the creep properties of second-generation Ni-based single crystal superalloys by composition optimization of Mo, W and Ti [J]. Mater. Sci. Eng., 2021, A799: 140163
20
Chen M K, Xie J, Shu D L, et al. Effect of long-term thermal exposures on tensile behaviors of K416B nickel-based superalloy [J]. Acta Metall. Sin. (Engl. Lett.), 2020, 33: 1699
doi: 10.1007/s40195-020-01075-3
21
Bao H S, Yang G, Chen Z Z, et al. Effects of long-term aging on microstructure and properties of a tungsten bearing heat-resistant alloy [J]. J. Iron Steel Res. Int., 2020, 27: 477
doi: 10.1007/s42243-020-00391-3
22
Lifshitz I M, Slyozov V V. The kinetics of precipitation from supersaturated solid solutions [J]. J. Phys. Chem. Solids, 1961, 19: 35
doi: 10.1016/0022-3697(61)90054-3
23
Pyczak F, Devrient B, Mughrabi H. The effects of different alloying elements on the thermal expansion coefficients, lattice constants and misfit of nickel-based superalloys investigated by X-ray diffraction [A]. Superalloys 2004 [C]. Warrendale, PA: TMS, 2004: 827
24
Baldan A. Review progress in Ostwald ripening theories and their applications to the γ'-precipitates in nickel-base superalloys Part II Nickel-base superalloys [J]. J. Mater. Sci., 2002, 37: 2379
doi: 10.1023/A:1015408116016
25
Thornton K, Akaiwa N, Voorhees P W. Large-scale simulations of Ostwald ripening in elastically stressed solids: I. Development of microstructure [J]. Acta Mater., 2004, 52: 1353
doi: 10.1016/j.actamat.2003.11.037
26
Sun W, Qin X Z, Guo J T, et al. Degeneration process and mechanism of primary MC carbides in a cast Ni-based superalloy [J]. Acta Metall. Sin., 2016, 52: 455
Xiao X, Zeng C, Hou J S, et al. The decomposition behavior of primary MC carbide in nickel base directionally solidified superalloy DZ444 [J]. Acta Metall. Sin., 2014, 50: 1031
Cui L Q. Investigation of microstructures and mechanical properties of M951G nickel-base superalloy [D]. Shenyang: University of Science and Technology of China (Institute of Metal Research, CAS), 2019
Pollock T M, Argon A S. Creep resistance of CMSX-3 nickel base superalloy single crystals [J]. Acta Metall. Mater., 1992, 40: 1
doi: 10.1016/0956-7151(92)90195-K
30
Shi Z X, Liu S Z, Zhao J Q. Effect of C content on microstructures and stress rupture properties of a single crystal superalloy [J]. Nonferrous Met. Mater. Eng., 2018, 39(5): 1
