Effect of Ti on the Corrosion Behavior of Fe22Cr5Al3Mo Alloy in 500oC Superheated Steam
SUN Rongrong1, YAO Meiyi1(), LIN Xiaodong1(), ZHANG Wenhuai1, QIU Yunlong2, HU Lijuan1, XIE Yaoping1, YANG Jian3, DONG Jianxin4, CHENG Guoguang5
1.Institute of Materials, Shanghai University, Shanghai 200072, China 2.Zhongxing Energy Equipment Co., Ltd., Haimen 226126, China 3.State Key Laboratory of Advanced Special Steel, School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China 4.School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 5.State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
SUN Rongrong, YAO Meiyi, LIN Xiaodong, ZHANG Wenhuai, QIU Yunlong, HU Lijuan, XIE Yaoping, YANG Jian, DONG Jianxin, CHENG Guoguang. Effect of Ti on the Corrosion Behavior of Fe22Cr5Al3Mo Alloy in 500oC Superheated Steam. Acta Metall Sin, 2022, 58(5): 610-622.
Zirconium alloys can react with water to produce hydrogen under a loss of coolant accident, which can lead to a hydrogen explosion. Therefore, the idea of developing accident tolerant fuel (ATF) is proposed, which involves nuclear fuel and cladding. FeCrAl alloy is a promising candidate material for ATF cladding. Studying the effects of alloying elements on the corrosion behavior and mechanism of FeCrAl alloy can provide a theoretical basis and guidance for optimizing its composition. Therefore, in this study, the effect of Ti on the corrosion behavior of Fe22Cr5Al3Mo alloy in 500oC superheated steam was investigated. Three types of Fe22Cr5Al3Mo-xTi (x = 0, 0.5, 1.0, mass fraction, %) alloys, designated as 0Ti, 0.5Ti, and 1.0Ti alloys, respectively, were fabricated and corroded in 500oC and 10.3 MPa superheated steam using a static autoclave. The microstructure, crystal structure and composition of the samples before and after corrosion were observed using XRD, OM, FIB/SEM, EDS, and TEM. The results show that the oxide films formed on the Fe22Cr5Al3Mo-xTi alloys in 500oC and 10.3 MPa superheated steam present a trilayer structure consisting of an outer oxide layer of Fe2O3, a middle layer of hcp-Cr2O3, and an inner layer of Al2O3. There is α-(Fe, Cr) in the Al2O3 layer near the oxide/metal interface. The ratio, R, of Cr oxide film thickness to total oxide film thickness for 0Ti, 0.5Ti, and 1.0Ti alloys follows the order R0.5Ti > R1.0Ti > R0Ti, which may explain the better corrosion resistance of 0.5Ti alloy than 1.0Ti and 0Ti alloys. The addition of Ti can reduce the total thickness of the oxide films and improve the corrosion resistance of the alloys by increasing the thickness of the protective hcp-Cr2O3 film and inhibiting the precipitation of Cr23C6.
Table 1 Compositions of alloys used in the present work
Fig.1 OM images of 0Ti (a), 0.5Ti (b), and 1.0Ti (c) alloys
Fig.2 XRD spectra of 0Ti, 0.5Ti, and 1.0Ti alloys
Alloy
Crystal plane index (hkl)
/ nm
(110)
(200)
(211)
2θ / (°)
d / nm
2θ / (°)
d / nm
2θ / (°)
d / nm
α-Fe
44.67
0.20268
65.02
0.14332
82.33
0.11702
0.28664
0Ti
44.15
0.20495
64.24
0.14487
81.45
0.11807
0.28960
0.5Ti
44.18
0.20482
64.24
0.14487
81.42
0.11810
0.28956
1.0Ti
44.28
0.20439
64.36
0.14463
81.42
0.11810
0.28920
Table 2 XRD characteristic peak parameters (the diffraction half angle of θ, the interplanar crystal spacing of d) and average lattice constant () of α-Fe, 0Ti, 0.5Ti, and 1.0Ti alloys
Fig.3 TEM images (a1-a6) and SAED patterns of P1-P6 (b1-b6) of typical second phase particles in 0Ti (a1, a2), 0.5Ti (a3, a4), and 1.0Ti (a5, a6) alloys (fcc—face centered cubic, o—orthorhombic, hcp—hexagonal close packed, c—primitive cubic, mc—base centered monoclinic)
Alloy
fcc-Cr23C6
o-Cr3C2
o-Fe3C
hcp-Fe2Ti
c-(Fe, Cr)
mc-Al8Mo3
fcc-TiN
0Ti
100-200
100
300
-
-
-
-
0.5Ti
-
100-200
80
100-150
150
150
350
1.0Ti
-
70-120
50-100
-
120
250-400
240
Table 3 Statistics of size for typical second phase particles in 0Ti, 0.5Ti, and 1.0Ti alloys
Fig.4 EDS mappings of TiN in the matrix of 0.5Ti (a) and 1.0Ti (b) alloys corroded in 500oC and 10.3 MPa superheated steam for 1000 h
Fig.5 SEM images of surface morphologies of oxide films formed on 0Ti (a1[24]-a3), 0.5Ti (b1-b3), and 1.0Ti (c1-c3) alloys corroded in 500oC and 10.3 MPa superheated steam for 3 h (a1[24]-c1), 500 h (a2-c2), and 1000 h (a3-c3)
Fig.6 HAADF images of the cross-sectional oxide films formed on the 0Ti (a1[24], a2[24], a3), 0.5Ti (b1-b3), and 1.0Ti (c1-c3) alloys corroded in 500oC and 10.3 MPa superheated steam for 3 h (a1[24]-c1), 500 h (a2[24]-c2), and 1000 h (a3-c3)
Alloy
3 h
500 h
1000 h
0Ti
250 ± 100
600 ± 30
720 ± 50
0.5Ti
60 ± 25
180 ± 85
330 ± 80
1.0Ti
60 ± 20
230 ± 65
370 ± 50
Table 4 Average thicknesses of oxide films formed on the 0Ti, 0.5Ti, and 1.0Ti alloys corroded in 500oC and 10.3 MPa superheated steam for 3 h, 500 h, and 1000 h
Fig.7 HAADF image and EDS mappings of cross-sectional oxide film formed on 0.5Ti alloy corroded in 500oC and 10.3 MPa superheated steam for 1000 h
Fig.8 TEM images and SAED patterns of different areas (insets) in the cross-sectional oxide films formed on 0Ti (a), 0.5Ti (b-f), and 1.0Ti (g) alloys corroded in 500oC and 10.3 MPa superheated steam for 500 h (a-c, g) and 1000 h (d-f) (m—monoclinic, bcc—body centered cubic)
Alloy
Oxide position
3 h
500 h
1000 h
0Ti
O
hcp-Fe2O3
hcp-Fe2O3
hcp-Fe2O3
M
-
-
hcp-Cr2O3
I
-
m-Al2O3
-
0.5Ti
O
hcp-Fe2O3
hcp-Fe2O3
hcp-Fe2O3
M
hcp-Cr2O3
hcp-Cr2O3
hcp-Cr2O3
I
hcp-Al2O3
o-Al2O3
o-Al2O3
1.0Ti
O
-
-
hcp-Fe2O3
M
hcp-Cr2O3
hcp-Cr2O3
hcp-Cr2O3
I
-
hcp-Al2O3
hcp-Al2O3
Table 5 Crystal structures of oxide films formed on 0Ti, 0.5Ti, and 1.0Ti alloys corroded in 500oC and 10.3 MPa super-heated steam for 3 h, 500 h, and 1000 h
Fig.9 Schematics of corrosion process of FeCrAl alloys in 500oC and 10.3 MPa superheated steam (a) Fe2O3 is preferentially formed on the thin original mixed layer of oxides (b) the mixed oxide region of Cr and Al is formed (c) Cr2O3 formed at the interface between Fe2O3 and the mixed oxide region of Cr and Al, while the Al2O3 formed at the O/M interface (d) unoxidized Fe and Cr near O/M interface exist in the form of α-(Fe, Cr)
Alloy
Iron oxide
Chromium oxide
Aluminum oxide
Overlap area
0Ti
220
40
80
260
0.5Ti
60
65
32
23
1.0Ti
80
65
60
25
Table 6 Average thicknesses of iron oxide film, chromium oxide film, aluminum oxide film, and overlap area formed on the 0Ti, 0.5Ti, and 1.0Ti alloys corroded in 500oC and 10.3 MPa superheated steam for 500 h
Time / h
0Ti
0.5Ti
1.0Ti
3
~0
0.133
0.083
500
0.067
0.361
0.283
1000
0.09
0.348
0.176
Table 7 Ratios of chromium oxide film thickness to total oxide film thickness for the 0Ti, 0.5Ti, and 1.0Ti alloys corroded in 500oC and 10.3 MPa super-heated steam for 3 h, 500 h, and 1000 h
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