Element Segregation in GH4169 Superalloy Large-Scale Ingot and Billet Manufactured by Triple-Melting
ZHANG Yong1, LI Xinxu1, WEI Kang1, WEI Jianhuan1, WANG Tao1, JIA Chonglin1, LI Zhao1, MA Zongqing2()
1 Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China 2 School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China
Cite this article:
ZHANG Yong, LI Xinxu, WEI Kang, WEI Jianhuan, WANG Tao, JIA Chonglin, LI Zhao, MA Zongqing. Element Segregation in GH4169 Superalloy Large-Scale Ingot and Billet Manufactured by Triple-Melting. Acta Metall Sin, 2020, 56(8): 1123-1132.
GH4169 has the advantage of excellent comprehensive mechanical properties, good oxidation and corrosion resistance, etc., which have been widely used in aero engine with the largest consumption. The GH4169 parts include high pressure compressor disk, turbine disk, shaft, gearbox and forged blade, et al. With the development of technology and the requirement of cost reducing, the size of GH4169 ingot and billet increases gradually at home and abroad. However, element segregation becomes more and more severe as the size of GH4169 ingot and billet increases, which will significantly degrade their mechanical properties. In this work, the large-scale GH4169 superalloy ingot (diameter 508 mm) was prepared by triple smelting, vacuum induction melting (VIM)+electro sag remelting (ESR)+vacuum arc remelting (VAR). Then, large-scale GH4169 billet (diameter 240 mm) was obtained from this prepared ingot via two-step high temperature homogenization heat treatment and cogging-forging. The element composition and microstructure at different positions of these large-scale ingot and billet were analyzed by SEM, TEM, EPMA and EDS. The results show that the segregation degree of element Al in GH4169 ingot is small, while those of elements Nb, Ti and Mo are large. Moreover, a lot of secondary phases were precipitated at the interdendritic regions of GH4169 ingot, including MC, Laves and δ phase. In the GH4169 billet prepared in our work, no "freckle" or "white spot" macro segregation was recognized, and the micro-element segregation was eliminated. Furthermore, combined with computational simulation, the chemical composition uniformity and main mechanical properties of GH4169 and Inconel 718 billets were compared. The statistical analysis using sample variance of macro chemical composition shows that the uniformity of chemical composition in GH4169 billet produced by different manufactures is different. The regional element segregation results in some vacillation on the mechanical properties of GH4169 billet. It is proposed that this regional element segregation can be further depressed by elaborately controlling the triple melting process and optimizing the homogenization heat treatment and forging process.
Fund: National Natural Science Foundation of China(51822404);GH4169 Superalloy 319 Special Item of Defense Science and Industry Bureua(XXZX-16-00X);Science and Technology Program of Tianjin(18YFZCGX00070)
Table 1 Main chemical compositions of triple smelted GH4169 and Inconel 718 alloys
Fig.1 SEM images of dendrite structures in different locations of GH4169 vacuum arc remelting (VAR) ingot (a) edge (b) R/2 (R refer to the VAR ingot radius 254 mm) (c) center
Position of ingot
Region
Al
Ti
Nb
Mo
Edge
Interdendritic region
Dendritic arm
0.457
0.491
1.249
0.910
6.082
3.376
3.160
2.768
R/2
Interdendritic region
Dendritic arm
0.477
0.513
1.256
0.846
6.442
2.870
2.964
2.545
Center
Interdendritic region
Dendritic arm
0.452
0.526
1.329
0.752
6.639
2.494
3.110
2.501
Table 2 Element distributions in different locations of VAR ingot of GH4169 alloy
Position of ingot
Al
Ti
Nb
Mo
Edge
1.074
0.729
0.555
0.876
R/2
1.075
0.674
0.446
0.857
Center
1.164
0.566
0.376
0.804
Table 3 Segregation coefficients (k) of elements in different locations of VAR ingot of GH4169 alloy
Fig.2 EPMA (a) and SEM (b) images of precipitated phase at center in VAR ingot of GH4169 alloy
Phase type
Al
Ti
Cr
Nb
Ni
Mo
Fe
C
Carbide
-
4.994
1.043
87.617
2.527
1.579
0.523
9.730
Laves phase
0.140
0.812
14.906
30.151
34.107
12.630
14.065
0.247
δ phase
0.272
1.905
11.651
15.972
58.570
2.344
11.214
-
Table 4 Chemical compositions of precipitated phase in VAR ingot of GH4169
Fig.3 SEM image and element distributions at center in VAR ingot of GH4169 alloy Color online
Fig.4 Calculated distributions of typical elements Nb (a), Mo (b), Al (c) and Ti (d) in VAR ingot of GH4169 alloy Color online
Fig.5 Calculated distributions of elements Nb (a), Mo (b), Al (c) and Ti (d) in VAR ingot of GH4169 alloy after homogenization heat treatment
Fig.6 TEM images of GH4169 billet (a) TEM image of grain boundary and second phase (b) HRTEM image of strengthening phase γ'' and matrx γ (c) SAED pattern of matrix, γ' and γ''
Fig.7 Distributions of typical elements Nb, Mo, Al, Ti and Cr in GH4169 billet Color online
Fig.8 SEM images of GH4169 billet at different locations (a) edge (b) R/2 (c) center
Position of billet
Al
Ti
Mo
Nb
Ni
Cr
Fe
Edge
0.453
1.089
2.758
4.875
54.393
18.798
19.266
0.427
1.044
2.801
4.778
54.658
18.796
19.508
0.411
1.051
2.803
4.771
54.325
18.796
19.421
Average value
0.430
1.061
2.787
4.808
54.459
18.797
19.398
R/2
0.440
1.094
2.740
4.975
53.962
19.172
19.298
0.502
1.122
2.742
4.835
53.877
19.225
19.312
0.488
1.109
2.716
4.870
54.178
19.098
19.268
Average value
0.477
1.108
2.733
4.893
54.006
19.165
19.293
Center
0.482
1.165
3.008
5.029
54.515
18.818
19.203
0.444
1.147
3.024
5.191
54.483
18.781
18.964
0.452
1.149
2.941
5.133
54.442
18.957
19.115
Average value
0.459
1.154
2.991
5.118
54.480
18.852
19.094
Table 5 Element distributions at different locations in GH4169 billet through EPMA
Fig.9 Element testing method at different locations in billet cross section (a) and the calculated results of standard deviation for GH4169 and Inconel 718 billets (b)
Fig.10 Brinell hardnesses at different locations of GH4169 and Inconel 718 billets
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