Softening Mechanism and Hydrogen Permeability of Rare Earth Y-Doped V-Cr Alloys
YANG Bo1, CHEN Xiaoliang1, SHI Xiaobin1, REN Wei2,3, GAO Heng3, SONG Guangsheng1()
1 Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials, Ministry of Education, School of Materials Science and Engineering, Anhui University of Technology, Ma'anshan 243032, China 2 State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200444, China 3 International Center for Quantum and Molecular Structures, Physics Department, College of Sciences, Shanghai University, Shanghai 200444, China
Cite this article:
YANG Bo, CHEN Xiaoliang, SHI Xiaobin, REN Wei, GAO Heng, SONG Guangsheng. Softening Mechanism and Hydrogen Permeability of Rare Earth Y-Doped V-Cr Alloys. Acta Metall Sin, 2025, 61(6): 887-899.
V100 - x Cr x (x = 8 or 10, atomic fraction, %) hydrogen-separation alloys undergo cracks during cold rolling and are difficult to be shaped via room temperature processing. However, the addition of rare-earth element Y can greatly improve their cold-rolling plastic deformation ability, facilitating the low-cost fabrication of V-based alloy membranes for hydrogen separation with high flux on a large scale. In order to achieve both high hydrogen-permeation efficiency and service life, insight into the hydrogen permeability and hydrogen-embrittlement resistance is required on the basis of excellent cold-rolling formability. In this work, the effects of Y addition on the microstructure, cold-rolling formability, hydrogen permeability, and hydrogen-embrittlement resistance of as-cast V100 - x - y Cr x Y y (x = 8, y = 1; x = 10, y = 0, 1, 3) hydrogen-separation alloys were studied using an oxygen-nitrogen-hydrogen analyzer, a cold-rolling machine, a hardness tester, a tension machine, and a hydrogen-permeation device as well as via XRD, SEM, TEM, and EPMA. In addition, the causes of the embrittlement of the V100 - x Cr x alloys and plasticization mechanism of V-Cr-Y alloys were explained. The microstructure formation and hydrogen-embrittlement resistance of V-Cr and V-Cr-Y alloys were also analyzed. Results showed that V-Cr alloys show a single-phase equiaxed grain microstructure, while V-Cr-Y alloys show a composite microstructure comprising a dendritic solid solution and secondary-phase particles located in the inter-dendritic region. The addition of Y in binary V-Cr alloys remarkably reduces the hardness, thereby greatly improving cold-rolling formability. Among the V91Cr8Y1, V89Cr10Y1, and V87Cr10Y3 alloys, V91Cr8Y1 showed the lowest hardness (108.88 HV) and highest maximum cold-rolling reduction rate (94.5%). Although the hydrogen permeability of the V-Cr-Y alloys was lower than those of Y-free alloys, it was still 2.5-3.0 times higher than those of commercial Pd77Ag23 alloys. Moreover, the V-Cr-Y alloys showed much better hydrogen-embrittlement resistance than those of V-Cr alloys and could be slowly cooled to room temperature without rupture. Rare-earth metal Y as a scavenger could react with O and S to form secondary-phase particles, exerting a purification effect, which softened the matrix and reduced the resistance of alloys to plastic deformation. Thus, high-performance V-Cr-Y alloy membranes with an excellent combination of formability and hydrogen-embrittlement resistance were prepared.
Fund: National Natural Science Foundation of China(51875002);Open Project of State Key Laboratory of Advanced Special Steel, Shanghai Key Laboratory of Advanced Ferrometallurgy(SKLASS 2022-13);Science and Technology Commission of Shanghai Municipality(19DZ2270200);Open Project of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(GFST2022KF08)
Corresponding Authors:
SONG Guangsheng, professor, Tel: 13329182538, E-mail: song_ahut@163.com
Fig.1 Schematic of tensile specimen size at room temperature (unit: mm)
Fig.2 Schematic of hydrogen permeation device (MFC—mass flow controller)
Fig.3 XRD spectra of as-cast V alloys (Dash lines show the pure vanadium diffraction peaks)
Fig.4 SEM images of as-cast V92Cr8 (a), V90Cr10 (b), V91Cr8Y1 (c), V89Cr10Y1 (d), and V87Cr10Y3 (e) alloys (Insets in Figs.4c-e show the corresponding high magnified images)
Fig.5 TEM image of grain boundary in as-cast V90Cr10 alloy (a), EDS line scan of grain boundary (b), HRTEM image (c), and fast Fourier transform (FFT) map corresponding to Fig.5c (d)
Fig.6 TEM images of phase boundary (a1) and matrix and Y-rich phase (b1) in as-cast V87Cr10Y3 alloy; EDS line scan from matrix to rich Y-phase in Fig.6a1 (a2); HRTEM images (b2, b3); and FFT maps (c1-c3)
Fig.7 BSE image of as-cast V87Cr10Y3 alloy (a) and EPMA mappings of V (b), Cr (c), Y (d), O (e), and S (f)
Point
V
Cr
Y
O
S
1
0.745
0
84.471
14.784
0
2
1.462
0
98.100
0.437
0
3
86.631
13.369
0
0
0
Table 1 EPMA point scan results obtained from points 1-3 in Fig.7a
Fig.8 Cold rolling schematic (a), cold-rolled sample photograph (b), and OM images of cold-rolled V92Cr8 (c), V90Cr10 (d), V91Cr8Y1 (e), V89Cr10Y1 (f), and V87Cr10Y3 (g) alloys (ND—normal direction, RD—rolling direction, TD—transverse direction)
Fig.9 Low (a, c) and high (b, d) magnified SEM images of tensile fracture of as-cast V90Cr10 (a, b) and V87Cr10Y3 (c, d) alloys (Inset in Fig.9d shows the stress-strain curve of V87Cr10Y3 alloy)
Fig.10 Vickers hardnesses and nanoindentation hardnesses of matrix (a) and maximum cold-rolling reduction rate (b) of as-cast V-Cr and V-Cr-Y alloys
Fig.11 Hydrogen permeability of as-cast V-Cr, V-Cr-Y, and Pd77Ag23[33] alloy membranes at 400 oC
Fig.12 Hydrogen permeation curves of as-cast V-Cr and V-Cr-Y alloy membranes obtained at a slow cooling rate of 2.5 oC/min and hydrogen pressure difference of 0.7 MPa
Fig.13 Optical images showing surface integrity of hydrogen permeated membranes of V-Cr and V-Cr-Y alloys (a) V92Cr8 (b) V90Cr10 (c) V91Cr8Y1 (d) V89Cr10Y1 (e) V87Cr10Y3
Fig.14 Gibbs free energy changes (ΔG) of oxides (a) and sulfides (b) of V, Cr, and Y
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