Effects of Processing on Microstructures and Properties of FGH4097 Superalloy
XIE Leipeng, SUN Wenyao(), CHEN Minghui(), WANG Jinlong, WANG Fuhui
Shenyang National Laboratory for Materials Science, Northeastern University, Shenyang 110819, China
Cite this article:
XIE Leipeng, SUN Wenyao, CHEN Minghui, WANG Jinlong, WANG Fuhui. Effects of Processing on Microstructures and Properties of FGH4097 Superalloy. Acta Metall Sin, 2022, 58(8): 992-1002.
Powder metallurgy (PM) nickel-based superalloys are widely used as high-temperature, fatigue-resistant components in aircraft and gas turbines. However, many powder particle boundaries and carbides are found in alloys prepared via traditional methods, such as hot pressing (HP) and hot isostatic pressing, causing serious damage to the properties of PM superalloys. New methods and processes must be developed to improve the performance of PM superalloys. SEM, EBSD, and TEM were used in this work to investigate the microstructure, mechanical properties, and oxidation behavior of FGH4097 alloys prepared via spark plasma sintering (SPS) and HP. Owing to the advantages of uniform microstructure, fine grain, and less carbide precipitation, SPSed alloy has better tensile properties and oxidation resistance than HPed alloy. At 25oC, SPSed alloy's yield, tensile strengths, and elongation are 998 MPa, 1401 MPa, and 17.1%, respectively; whereas those of HPed alloy are 951 MPa, 1262 MPa, and 14.4%, respectively. Although the two alloys exhibit similar yield and tensile strengths at 700oC, SPSed alloy shows merely 80% higher ductility than HPed alloy. The oxidation mass gain of the two alloys oxidized at 900oC for 100 h follows the parabolic law. A continuous and dense Al2O3 scale is formed on the surface of SPSed alloy, which effectively prevents the inward diffusion of O and outward diffusion of Cr and Ti. The mass gain is merely 0.19 mg/cm2, and the oxidation rate is 1.03 × 10-7 mg2/(cm4·s). Conversely, the oxidation rate of HPed alloy is approximately 2.6 times that of SPSed alloy. Severe internal oxidation occurs in HPed alloy, resulting in abundant less protective NiCr2O4 and TiO2 formation on the surface, as well as large cracks and spalling.
Fig.1 SEM image of FGH4097 pre-alloy powder (Inset shows the dendrite structure in powder)
Fig.2 Low (a, c) and high (b, d) magnified backscattered electron (BSE) images of FGH4097 alloys prepared by hot pressing (HP) (a, b) and spark plasma sintering (SPS) (c, d) (PPB—powder particle boundary)
Fig.3 BF-STEM images (a-d) of FGH4097 alloys prepared by HP (a, b) and SPS (c, d), and selected area electron diffraction (SAED) patterns for region 3 in Fig.3b (e) and region 5 in Fig.3c (f), respectively
Region
C
Ti
Nb
W
Mo
Hf
O
Ni
Co
Cr
Al
1
4.33
1.11
11.28
9.85
34.56
0
2.66
11.28
5.05
28.05
1.59
2
35.40
18.76
38.57
0.74
0.54
0.76
0
2.81
0.91
1.34
0.16
3
41.52
18.84
34.32
0.52
0
1.31
0
1.91
0.66
0.86
0.06
4
0
1.67
0
0.23
0.69
30.11
37.52
18.51
6.31
1.96
0
5
0
0.24
0
0
0
36.06
47.76
9.29
2.80
3.97
0
6
31.56
20.43
41.31
0.10
0.41
1.17
0
3.18
0.55
1.29
0
Table 1 EDS results of regions 1-6 in Fig.3
Fig.4 EBSD images (a, c) and grain size distributions (b, d) of FGH4097 alloys prepared by HP (a, b) and SPS (c, d)
Fig.5 Engineering stress-strain curves of FGH4097 alloys prepared by HP and SPS (a) 25oC (b) 700oC
Fig.6 Fracture surface (a, b) and cross-sectional (c-f) morphologies of FGH4097 alloys prepared by HP (a, c, e) and SPS (b, d, f) after tensile test at 25oC (GB—grain boundary)
Fig.7 Isothermal oxidation kinetics of the FGH4097 alloys prepared by HP and SPS at 900oC for 100 h (y—oxidation weight gain per unit area, t—oxidation time, kp—rate constant of the parabola, y2 = kpt) (a) y vs t (b) y2vs t
Fig.8 XRD spectra of FGH4097 alloys prepared by HP and SPS after oxidation at 900oC for 100 h
Fig.9 Surface (a, b) and cross-sectional (c-f) SEM images of FGH4097 alloys prepared by HP (a, c, e) and SPS (b, d, f) after oxidation at 900oC for 100 h
Sample
σp
σd
σs
Theoretical value
Ture value
HPed
389
144
210
743
951
SPSed
448
209
210
867
998
Table 2 Contributions of each strengthening mechanism to the yield strength of HPed and SPSed FGH4097 alloys
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