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Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys
Journal Pre-proofs Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys Jie Wu, Ping Lu, Lei Dong, Mengli Zhao, Dejun Li, Wenbin Xue PII: DOI: Reference:
S0167-577X(19)31712-4 https://doi.org/10.1016/j.matlet.2019.127080 MLBLUE 127080
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
29 July 2019 24 October 2019 25 November 2019
Please cite this article as: J. Wu, P. Lu, L. Dong, M. Zhao, D. Li, W. Xue, Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127080
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys Jie Wu1, Ping Lu1, Lei Dong1, Mengli Zhao1, Dejun Li1*, Wenbin Xue2* 1 College
of Physics and Materials Science, Tianjin Normal University, Tianjin, 300387, China
2College
of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China
Abstract In this paper, the plasma electrolytic oxidation (PEO) and pulsed laser deposition (PLD) methods were combined for the preparation of ZrO2 and Cr/CrN/Cr2O3 composite film on Zr-4 alloy. The PEO process was carried out in the alkaline electrolyte containing KOH and Na3PO4. For the PLD process, a Cr2N target was decomposed to CrN and Cr, and the latter is partially oxidized under the background gas of oxygen to form a Cr/CrN/Cr2O3 film. The composite film exhibits excellent corrosion resistance at high temperature. This work provides a methodological guidance for the preparation of composite film on zirconium alloys, which are usually used as structural materials in the nuclear industry. Keywords: Oxidation; Ceramic composites; Zirconium alloys; High temperature corrosion * Corresponding author. E-mail: [email protected] (D. Li), [email protected] (W. Xue). 1. Introduction Zirconium alloys such as Zr-4, Zr-1Nb and ZIRLO have been widely used as nuclear fuel cladding materials in reactors due to their low neutron capture cross sections, good corrosion resistance and mechanical properties at high temperature [1-3]. In recent years, the safety and reliability of nuclear power plant operation has drawn increased attention especially after the
1
Fukushima accident. Yet, the deep burnup trend of fuel assembly is exposing the zirconium alloys to a more corrosive condition with high-temperature steam or air. In response, some new materials such as SiC-based ceramic composites [4] and Nb, Mo based alloys [5] have been designed to replace zirconium alloys. However, it is easier and more economical to apply coating technology to zirconium cladding to obtain protection capability without a change in the base materials. Thus, seeking an appropriate surface modification method for zirconium alloys to improve the corrosion resistance has important practical significance. Plasma electrolytic oxidation (PEO), based on plasma discharge phenomenon in aqueous solution at room temperature and atmosphere pressure, is an efficient method to fabricate oxide ceramic films on zirconium and its alloys [6,7]. A thick ZrO2 film can be formed in a few minutes, but the film surface presents a porous morphology, which is not beneficial for the further improvement of corrosion resistance. Pulsed laser deposition (PLD) is a versatile thin film growth method, where the ejected high energy particles from the target with the help of laser plume can largely contribute to the improvement of crystalline quality of the film even at a low temperature. The prepared film usually presents excellent uniformity with a fine grain size in nanoscale, but the preparation efficiency is much lower than PEO process and the preparation cost is higher since it is carried out under vacuum condition. It is known that chromium and its compounds own excellent wear and corrosion resistance [8,9], which makes them ideal protective materials for metals. In this work, PLD was employed to prepare a chromium containing film on PEO treated Zr-4 alloy. The chromium covered ZrO2 composite film was expected to exhibit higher corrosion resistance with lower cost.
2
2. Experimental The Zr-4 alloy (Sn: 1.20~1.70, Fe: 0.18~0.24, wt.%, Zr balance) sheet of 1 mm thick was cut into coupons with 10 mm×25 mm dimensions. The specimens were mechanically polished with 1000-grit emery paper, followed by chemical polishing in a mixture acid and ultrasonical cleaning in acetone. For the PEO treatment, the Zr-4 alloy was set as the anode of a bipolar power supply, and a stainless steel container with electrolyte solution was connected to the cathode. The duty cycle of the power supply was 45%, and the pulse frequency was 150 Hz. The applied voltages were +450 V and -50 V. The electrolyte solution consists of 1 g/l KOH and 12 g/l Na3PO4, and the discharge time was 10 min. During the PEO treatment, the electrolyte solution was cooled by running water, and its temperature was maintained at about 25°C. After that, a ceramic ZrO2 film was fabricated on Zr-4 alloy. Then, the PEO treated Zr-4 alloy specimen was placed in the chamber of PLD device. The laser source of PLD was a pulsed KrF excimer laser operating at 248 nm with a 25 ns pulse width. The laser energy and repetition rate was held at 350 mJ per pulse and 5 Hz, respectively. The distance between substrate and Cr2N target was 40 mm. During the deposition process, the chamber was maintained at a vacuum degree of 3×10-5 Pa with the oxygen flux at 3 sccm, and the deposition time was 60 min. The microstructure and composition of the prepared composite film on Zr-4 alloy were analyzed by scanning electron microscope (SEM, Hitachi SU-8010), X-ray diffraction (XRD, Bruker D8A) and X-ray photoelectron spectroscopy (XPS, Thermofisher ESCALAB 250Xi). An electrochemical workstation (Princeton Applied Research, PARSTAT 2273) was connected to a dynamic high-temperature-high-pressure electrochemical system (Cortest, 3
AC200) to evaluate the corrosion resistance of the composite film at high temperture (300°C, 14MPa). The experimental solution was 2.3 ppm Li+ and 1500 ppm B3+ solution, which was often used in pressurized water reactor. 3. Results and discussion Fig.1 shows the cross-sectional SEM micrograph and line scanning composition profiles of the composite film on Zr-4 alloy. As shown in Fig.1a, the thickness of the ZrO2 film by PEO and the chromium compounds film by PLD are about 12 μm and 2 μm, respectively. In Fig.1b, it is obvious that the Zr content reduces while O content rises from the substrate to the ZrO2 film. Moreover, there are distinguishable increases for chromium, nitrogen and oxygen contents in the top layer of the composite film, which suggests a dense chromium compounds film has been covered on the ZrO2 film, blocking the pores and cavities on its surface. In general, a dense film is beneficial to prevent the substrate from corrosion [10]. Thus, the prepared composite film is expected to achieve better corrosion resistance. The increase of oxygen content may originate from the chromic oxide in the film due to the oxidation reaction under oxygen background gas. Fig.2a shows the θ-2θ scan and glancing angle XRD pattern of the composite film on Zr-4 alloy. Diffraction peaks at 37.5°, 43.7°, 63.5° and 76.1° respectively correspond to the (111), (200), (220) and (311) planes for the cubic CrN structure (PDF#11-0065). These results are consistent with the studies performed by Wang et al. [11,12] using other deposition method such as magnetron sputtering. In addition, monoclinic zirconia (m-ZrO2) phase (PDF#37-1484) and zirconium substrate (PDF#05-0665) are also identified in the θ-2θ scan XRD pattern, since the film is not thick enough to block the X-rays completely. Furthermore, 4
in the glancing angle XRD pattern, the diffraction peaks at 44.1° and 48.6° belong to metallic Cr (PDF#65-3316), while the diffraction peaks at 33.6° and 36.2° originate from Cr2O3 phase (PDF#38-1479). Fig.2b shows the XPS Cr2p3/2 spectrum of the film. It reveals that there are three Cr bonding states on the film surface, including Cr-N bond in CrN (575.2 eV), Cr-O bond in Cr2O3 (576.5 eV) and Cr metallic bond (574.1 eV) [12,13]. In light of the ratio of Cr-N peak area to the whole Cr2p3/2 peak area, the CrN content in the film is about 65.5%. Meanwhile, chromic oxide and metallic chromium also exist in the surface region, though their contents are too little to be detected by θ-2θ scan XRD. Thus, a composite film containing Cr, CrN and Cr2O3 has been prepared on the ZrO2 film. It turns out that the obtained surface composition is influenced not only by the target evaporation process but also by a decomposition of the Cr2N and an oxidation process. Fig.3a shows the potentiodynamic polarization curves of monolayer ZrO2 film on Zr-4 alloy by PEO and ZrO2 + Cr/CrN/Cr2O3 composite film by PEO and PLD at 300 °C in 2.3 ppm Li+ and 1500 ppm B3+ solution. Though the corrosion potentials (Ecorr) of both films are close to -0.4 V, the corrosion current density (icorr) of the composite film (4.83×10−5 A/cm2) is much lower than that of the monolayer ZrO2 film (1.22×10−4 A/cm2). This indicates that the composite film has better corrosion resistance and the Cr/CrN/Cr2O3 film has successfully sealed the top porous surface of ZrO2 film. Fig.3b-d shows the EIS Nyquist and Bode diagrams of two films. Comparing to the monolayer ZrO2 film, the diameter of capacitive loop in Fig.3b and the impedance modulus in Fig.3c of the composite film are both bigger, indicating a larger polarization resistance and better corrosion resistance. Moreover, the Nyquist diagram of the composite film exhibits two depressed semicircles, based on the 5
model fitting of double-layer structure. Correspondingly, in the phase angle vs. frequency curves (Fig.3d), there are two distinguishable peaks, which implies two time constants [14]. Furthermore, the phase angle maximum is related to the integrity and compactness of the film [15-17]. The higher phase angle maximum of the composite film suggests that it has a better compactness than the monolayer ZrO2 film. Therefore, the high corrosion resistance should be ascribed to the dense Cr/CrN/Cr2O3 film covering on the ZrO2 film, which acts as a good barrier against ion attack in reactor coolant with LiOH and H3BO3 effectively. 4. Conclusions In this work, PEO and PLD were combined for the preparation of ZrO2 and Cr/CrN/Cr2O3 composite film on Zr-4 alloy. Under the background gas of oxygen, the Cr2N target was locally evaporated and decomposed to CrN and Cr during the PLD process, and the metallic Cr was partially oxidized to Cr2O3. The dense Cr/CrN/Cr2O3 film can effectively seal the pores and cavities on the ZrO2 film surface, and thus the corrosion resistance under the high temperature and high pressure water environment was improved significantly. This work provides a viable approach for the preparation of composite film used as corrosion protection for zirconium alloys in nuclear reactor. Acknowledgments This research was sponsored by the Tianjin Natural Science Foundation (Nos. 18JCQNJC73400 and 18JCQNJC72000), the National Natural Science Foundation of China (Nos. 51901158 and 51772209), the Science & Technology Development Fund of Tianjin Education Commission for Higher Education (No. 2018KJ158), Program for Innovative Research in University of Tianjin (No. TD13-5077) and the Doctoral Foundation of Tianjin 6
Normal University (No. 52XB1606). References [1] A.T. Motta, A. Yilmazbayhan, M.J. Silva, R.J. Comstock, G.S. Was, J.T. Busby, E. Gartner, Q. Peng, Y.H. Jeong, J.Y. Park, J. Nucl. Mater. 371 (2007) 61-75. [2] Z. Zou, W. Xue, X. Jia, J. Du, R. Wang, L. Weng, Surf. Coat. Technol. 222 (2013) 62-67. [3] H. Yang, J. Shen, S. Kano, Y. Matsukawa, Y. Li, Y. Satoh, T. Matsunaga, H. Abe, Mater. Lett. 158 (2015) 88-91. [4] L. Hallstadius, S. Johnson, E. Lahoda, Prog. Nucl. Energy 57 (2012) 71-76. [5] A.T. Nelson, E.S. Sooby, Y.J. Kim, B. Cheng, S.A. Maloy, J. Nucl. Mater. 448 (2014) 441-447. [6] Y. Cheng, E. Matykina, P. Skeldon, G. Thompson, Electrochim. Acta 56 (2011) 8467-8476. [7] J. Wu, L. Chen, Y. Qu, L. Dong, J. Guo, D. Li, W. Xue, Surf. Coat. Technol. 359 (2019) 366-373. [8] Q.G. Zhou, X.D. Bai, X.W. Chen, D.Q. Peng, Y.H. Ling, Appl. Surf. Sci. 211 (2003) 293-299. [9] X. Guan, Y. Wang, G. Zhang, X. Jiang, L. Wang, Q. Xue, Tribol. Int. 106 (2017) 78-87. [10] J. Wu, Y. Zhang, R. Liu, B. Wang, M. Hua, W. Xue, Appl. Surf. Sci. 347 (2015) 673-678. [11] D. Wang, M. Hu, D. Jiang, X. Gao, Y. Fu, Q. Wang, J. Yang, Mater. Lett. 188 (2017) 267-270. [12] S. Gao, C. Dong, H. Luo, K. Xiao, X. Pan, X. Li, Electrochim. Acta 114 (2013) 233-241. [13] P. Yi, L. Peng, T. Zhou, J. Huang, X. Lai, J. Power Sources 236 (2013) 47-53. [14] H. Sun, X. Wu, E. Han, Y. Wei, Corros. Sci. 59 (2012) 334-342.. [15] J.B. Jorcin, M.E. Orazem, N. Pébère, B. Tribollet, Electrochim. Acta 51 (2006) 1473-1479. [16] S.L. Assis, S. Wolynec, I. Costa, Electrochim. Acta 51 (2006) 1815-1819. [17] Z.B. Wang, H.X. Hu, C.B. Liu, Y.G. Zheng, Electrochim. Acta 135 (2014) 526-535.
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Figures captions Figure 1. Cross-sectional SEM micrograph (a) and EDS line scanning composition profiles (b) of the ZrO2 + Cr/CrN/Cr2O3 composite film on Zr-4 alloy. Figure 2. (a) θ-2θ scan and glancing angle XRD pattern of the composite film on Zr-4 alloy, (b) XPS Cr2p3/2 spectrum of the composite film. Figure 3. Potentiodynamic polarization curves (a), EIS Nyquist plots (b), Bode plots of impedance modulus (c) and Bode plots of phase angle (d) of monolayer ZrO2 film and ZrO2 + Cr/CrN/Cr2O3 composite film at 300 °C in 2.3 ppm Li+ and 1500 ppm B3+ solution.
8
Fig. 1
(a)
I
ZrO2 film II
II
Cr/CrN/Cr2O3 film III
III
Zr O Cr N
Intensity /Arb. units
(b)
Zr-4 alloy substrate I
0
5
10
15
20
Distance /m
9
25
30
Fig. 2 ■
(a)
■
Zr ▼ ZrO 2
Cr2O3 Cr
Intensity /a.u.
▼
■
▼ ▼
▼ ▼ ▼ ■
■
glancing angle
■
▼ ▼▼
▼
■ CrN
▼ ▼ ▼
▼ ▼
▼
▼
▼
-2 scan 20
20000
40
(b)
Counts /s
16000
12000
60
80
2Theta /()
Experiment Fitted curve Background Peak 1 Peak 2 Peak 3
Cr 2p3/2 CrN
Cr2O3
metallic Cr
8000
4000
582
580
578
576
574
572
Binding Energy /eV
10
570
Fig. 3
0.0
ZrO2+Cr/CrN/Cr2O3 film
2
-0.2 ZrO2+Cr/CrN/Cr2O3 film
-0.4
500
ZrO2 film
-0.6
ZrO2 film 1E-7
1E-6
1E-5
1E-4
Current density (A·cm
0
1E-3
-2
)
2
|Z| (Ω cm )
ZrO2+Cr/CrN/Cr2O3 film
1000 ZrO2 film
100
-2
0
10
2
10
10
4
10
6
10
Frequency (Hz) 60
(d)
50
30
peak 2
peak 1
40 ZrO2 film
20 10 ZrO2+Cr/CrN/Cr2O3 film
0 -10 -2 10
0
10
2
10
Frequency (Hz)
0
1000
2000
3000 2
Z' （Ω·cm ）
(c)
10000
Phase angel (degree)
(b)
1000
-Z" (Ω·cm )
Potential (V, SCE)
1500
(a)
0.2
4
10
6
10
11
4000
5000
Conflicts of interest None.
12
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
13
Highlights 1. 2. 3. 4. 5.
A particular ZrO2 and Cr/CrN/Cr2O3 composite film was prepared. Cr2N was decomposed to CrN and Cr during the PLD process. The Cr/CrN/Cr2O3 film can seal the porous ZrO2 film surface. The composite film exhibits excellent corrosion resistance at high temperature. The corrosion current density of composite film is only 40% of single ZrO2.
14
S0167-577X(19)31712-4 https://doi.org/10.1016/j.matlet.2019.127080 MLBLUE 127080
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
29 July 2019 24 October 2019 25 November 2019
Please cite this article as: J. Wu, P. Lu, L. Dong, M. Zhao, D. Li, W. Xue, Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127080
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Combination of plasma electrolytic oxidation and pulsed laser deposition for preparation of corrosion-resisting composite film on zirconium alloys Jie Wu1, Ping Lu1, Lei Dong1, Mengli Zhao1, Dejun Li1*, Wenbin Xue2* 1 College
of Physics and Materials Science, Tianjin Normal University, Tianjin, 300387, China
2College
of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China
Abstract In this paper, the plasma electrolytic oxidation (PEO) and pulsed laser deposition (PLD) methods were combined for the preparation of ZrO2 and Cr/CrN/Cr2O3 composite film on Zr-4 alloy. The PEO process was carried out in the alkaline electrolyte containing KOH and Na3PO4. For the PLD process, a Cr2N target was decomposed to CrN and Cr, and the latter is partially oxidized under the background gas of oxygen to form a Cr/CrN/Cr2O3 film. The composite film exhibits excellent corrosion resistance at high temperature. This work provides a methodological guidance for the preparation of composite film on zirconium alloys, which are usually used as structural materials in the nuclear industry. Keywords: Oxidation; Ceramic composites; Zirconium alloys; High temperature corrosion * Corresponding author. E-mail: [email protected] (D. Li), [email protected] (W. Xue). 1. Introduction Zirconium alloys such as Zr-4, Zr-1Nb and ZIRLO have been widely used as nuclear fuel cladding materials in reactors due to their low neutron capture cross sections, good corrosion resistance and mechanical properties at high temperature [1-3]. In recent years, the safety and reliability of nuclear power plant operation has drawn increased attention especially after the
1
Fukushima accident. Yet, the deep burnup trend of fuel assembly is exposing the zirconium alloys to a more corrosive condition with high-temperature steam or air. In response, some new materials such as SiC-based ceramic composites [4] and Nb, Mo based alloys [5] have been designed to replace zirconium alloys. However, it is easier and more economical to apply coating technology to zirconium cladding to obtain protection capability without a change in the base materials. Thus, seeking an appropriate surface modification method for zirconium alloys to improve the corrosion resistance has important practical significance. Plasma electrolytic oxidation (PEO), based on plasma discharge phenomenon in aqueous solution at room temperature and atmosphere pressure, is an efficient method to fabricate oxide ceramic films on zirconium and its alloys [6,7]. A thick ZrO2 film can be formed in a few minutes, but the film surface presents a porous morphology, which is not beneficial for the further improvement of corrosion resistance. Pulsed laser deposition (PLD) is a versatile thin film growth method, where the ejected high energy particles from the target with the help of laser plume can largely contribute to the improvement of crystalline quality of the film even at a low temperature. The prepared film usually presents excellent uniformity with a fine grain size in nanoscale, but the preparation efficiency is much lower than PEO process and the preparation cost is higher since it is carried out under vacuum condition. It is known that chromium and its compounds own excellent wear and corrosion resistance [8,9], which makes them ideal protective materials for metals. In this work, PLD was employed to prepare a chromium containing film on PEO treated Zr-4 alloy. The chromium covered ZrO2 composite film was expected to exhibit higher corrosion resistance with lower cost.
2
2. Experimental The Zr-4 alloy (Sn: 1.20~1.70, Fe: 0.18~0.24, wt.%, Zr balance) sheet of 1 mm thick was cut into coupons with 10 mm×25 mm dimensions. The specimens were mechanically polished with 1000-grit emery paper, followed by chemical polishing in a mixture acid and ultrasonical cleaning in acetone. For the PEO treatment, the Zr-4 alloy was set as the anode of a bipolar power supply, and a stainless steel container with electrolyte solution was connected to the cathode. The duty cycle of the power supply was 45%, and the pulse frequency was 150 Hz. The applied voltages were +450 V and -50 V. The electrolyte solution consists of 1 g/l KOH and 12 g/l Na3PO4, and the discharge time was 10 min. During the PEO treatment, the electrolyte solution was cooled by running water, and its temperature was maintained at about 25°C. After that, a ceramic ZrO2 film was fabricated on Zr-4 alloy. Then, the PEO treated Zr-4 alloy specimen was placed in the chamber of PLD device. The laser source of PLD was a pulsed KrF excimer laser operating at 248 nm with a 25 ns pulse width. The laser energy and repetition rate was held at 350 mJ per pulse and 5 Hz, respectively. The distance between substrate and Cr2N target was 40 mm. During the deposition process, the chamber was maintained at a vacuum degree of 3×10-5 Pa with the oxygen flux at 3 sccm, and the deposition time was 60 min. The microstructure and composition of the prepared composite film on Zr-4 alloy were analyzed by scanning electron microscope (SEM, Hitachi SU-8010), X-ray diffraction (XRD, Bruker D8A) and X-ray photoelectron spectroscopy (XPS, Thermofisher ESCALAB 250Xi). An electrochemical workstation (Princeton Applied Research, PARSTAT 2273) was connected to a dynamic high-temperature-high-pressure electrochemical system (Cortest, 3
AC200) to evaluate the corrosion resistance of the composite film at high temperture (300°C, 14MPa). The experimental solution was 2.3 ppm Li+ and 1500 ppm B3+ solution, which was often used in pressurized water reactor. 3. Results and discussion Fig.1 shows the cross-sectional SEM micrograph and line scanning composition profiles of the composite film on Zr-4 alloy. As shown in Fig.1a, the thickness of the ZrO2 film by PEO and the chromium compounds film by PLD are about 12 μm and 2 μm, respectively. In Fig.1b, it is obvious that the Zr content reduces while O content rises from the substrate to the ZrO2 film. Moreover, there are distinguishable increases for chromium, nitrogen and oxygen contents in the top layer of the composite film, which suggests a dense chromium compounds film has been covered on the ZrO2 film, blocking the pores and cavities on its surface. In general, a dense film is beneficial to prevent the substrate from corrosion [10]. Thus, the prepared composite film is expected to achieve better corrosion resistance. The increase of oxygen content may originate from the chromic oxide in the film due to the oxidation reaction under oxygen background gas. Fig.2a shows the θ-2θ scan and glancing angle XRD pattern of the composite film on Zr-4 alloy. Diffraction peaks at 37.5°, 43.7°, 63.5° and 76.1° respectively correspond to the (111), (200), (220) and (311) planes for the cubic CrN structure (PDF#11-0065). These results are consistent with the studies performed by Wang et al. [11,12] using other deposition method such as magnetron sputtering. In addition, monoclinic zirconia (m-ZrO2) phase (PDF#37-1484) and zirconium substrate (PDF#05-0665) are also identified in the θ-2θ scan XRD pattern, since the film is not thick enough to block the X-rays completely. Furthermore, 4
in the glancing angle XRD pattern, the diffraction peaks at 44.1° and 48.6° belong to metallic Cr (PDF#65-3316), while the diffraction peaks at 33.6° and 36.2° originate from Cr2O3 phase (PDF#38-1479). Fig.2b shows the XPS Cr2p3/2 spectrum of the film. It reveals that there are three Cr bonding states on the film surface, including Cr-N bond in CrN (575.2 eV), Cr-O bond in Cr2O3 (576.5 eV) and Cr metallic bond (574.1 eV) [12,13]. In light of the ratio of Cr-N peak area to the whole Cr2p3/2 peak area, the CrN content in the film is about 65.5%. Meanwhile, chromic oxide and metallic chromium also exist in the surface region, though their contents are too little to be detected by θ-2θ scan XRD. Thus, a composite film containing Cr, CrN and Cr2O3 has been prepared on the ZrO2 film. It turns out that the obtained surface composition is influenced not only by the target evaporation process but also by a decomposition of the Cr2N and an oxidation process. Fig.3a shows the potentiodynamic polarization curves of monolayer ZrO2 film on Zr-4 alloy by PEO and ZrO2 + Cr/CrN/Cr2O3 composite film by PEO and PLD at 300 °C in 2.3 ppm Li+ and 1500 ppm B3+ solution. Though the corrosion potentials (Ecorr) of both films are close to -0.4 V, the corrosion current density (icorr) of the composite film (4.83×10−5 A/cm2) is much lower than that of the monolayer ZrO2 film (1.22×10−4 A/cm2). This indicates that the composite film has better corrosion resistance and the Cr/CrN/Cr2O3 film has successfully sealed the top porous surface of ZrO2 film. Fig.3b-d shows the EIS Nyquist and Bode diagrams of two films. Comparing to the monolayer ZrO2 film, the diameter of capacitive loop in Fig.3b and the impedance modulus in Fig.3c of the composite film are both bigger, indicating a larger polarization resistance and better corrosion resistance. Moreover, the Nyquist diagram of the composite film exhibits two depressed semicircles, based on the 5
model fitting of double-layer structure. Correspondingly, in the phase angle vs. frequency curves (Fig.3d), there are two distinguishable peaks, which implies two time constants [14]. Furthermore, the phase angle maximum is related to the integrity and compactness of the film [15-17]. The higher phase angle maximum of the composite film suggests that it has a better compactness than the monolayer ZrO2 film. Therefore, the high corrosion resistance should be ascribed to the dense Cr/CrN/Cr2O3 film covering on the ZrO2 film, which acts as a good barrier against ion attack in reactor coolant with LiOH and H3BO3 effectively. 4. Conclusions In this work, PEO and PLD were combined for the preparation of ZrO2 and Cr/CrN/Cr2O3 composite film on Zr-4 alloy. Under the background gas of oxygen, the Cr2N target was locally evaporated and decomposed to CrN and Cr during the PLD process, and the metallic Cr was partially oxidized to Cr2O3. The dense Cr/CrN/Cr2O3 film can effectively seal the pores and cavities on the ZrO2 film surface, and thus the corrosion resistance under the high temperature and high pressure water environment was improved significantly. This work provides a viable approach for the preparation of composite film used as corrosion protection for zirconium alloys in nuclear reactor. Acknowledgments This research was sponsored by the Tianjin Natural Science Foundation (Nos. 18JCQNJC73400 and 18JCQNJC72000), the National Natural Science Foundation of China (Nos. 51901158 and 51772209), the Science & Technology Development Fund of Tianjin Education Commission for Higher Education (No. 2018KJ158), Program for Innovative Research in University of Tianjin (No. TD13-5077) and the Doctoral Foundation of Tianjin 6
Normal University (No. 52XB1606). References [1] A.T. Motta, A. Yilmazbayhan, M.J. Silva, R.J. Comstock, G.S. Was, J.T. Busby, E. Gartner, Q. Peng, Y.H. Jeong, J.Y. Park, J. Nucl. Mater. 371 (2007) 61-75. [2] Z. Zou, W. Xue, X. Jia, J. Du, R. Wang, L. Weng, Surf. Coat. Technol. 222 (2013) 62-67. [3] H. Yang, J. Shen, S. Kano, Y. Matsukawa, Y. Li, Y. Satoh, T. Matsunaga, H. Abe, Mater. Lett. 158 (2015) 88-91. [4] L. Hallstadius, S. Johnson, E. Lahoda, Prog. Nucl. Energy 57 (2012) 71-76. [5] A.T. Nelson, E.S. Sooby, Y.J. Kim, B. Cheng, S.A. Maloy, J. Nucl. Mater. 448 (2014) 441-447. [6] Y. Cheng, E. Matykina, P. Skeldon, G. Thompson, Electrochim. Acta 56 (2011) 8467-8476. [7] J. Wu, L. Chen, Y. Qu, L. Dong, J. Guo, D. Li, W. Xue, Surf. Coat. Technol. 359 (2019) 366-373. [8] Q.G. Zhou, X.D. Bai, X.W. Chen, D.Q. Peng, Y.H. Ling, Appl. Surf. Sci. 211 (2003) 293-299. [9] X. Guan, Y. Wang, G. Zhang, X. Jiang, L. Wang, Q. Xue, Tribol. Int. 106 (2017) 78-87. [10] J. Wu, Y. Zhang, R. Liu, B. Wang, M. Hua, W. Xue, Appl. Surf. Sci. 347 (2015) 673-678. [11] D. Wang, M. Hu, D. Jiang, X. Gao, Y. Fu, Q. Wang, J. Yang, Mater. Lett. 188 (2017) 267-270. [12] S. Gao, C. Dong, H. Luo, K. Xiao, X. Pan, X. Li, Electrochim. Acta 114 (2013) 233-241. [13] P. Yi, L. Peng, T. Zhou, J. Huang, X. Lai, J. Power Sources 236 (2013) 47-53. [14] H. Sun, X. Wu, E. Han, Y. Wei, Corros. Sci. 59 (2012) 334-342.. [15] J.B. Jorcin, M.E. Orazem, N. Pébère, B. Tribollet, Electrochim. Acta 51 (2006) 1473-1479. [16] S.L. Assis, S. Wolynec, I. Costa, Electrochim. Acta 51 (2006) 1815-1819. [17] Z.B. Wang, H.X. Hu, C.B. Liu, Y.G. Zheng, Electrochim. Acta 135 (2014) 526-535.
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Figures captions Figure 1. Cross-sectional SEM micrograph (a) and EDS line scanning composition profiles (b) of the ZrO2 + Cr/CrN/Cr2O3 composite film on Zr-4 alloy. Figure 2. (a) θ-2θ scan and glancing angle XRD pattern of the composite film on Zr-4 alloy, (b) XPS Cr2p3/2 spectrum of the composite film. Figure 3. Potentiodynamic polarization curves (a), EIS Nyquist plots (b), Bode plots of impedance modulus (c) and Bode plots of phase angle (d) of monolayer ZrO2 film and ZrO2 + Cr/CrN/Cr2O3 composite film at 300 °C in 2.3 ppm Li+ and 1500 ppm B3+ solution.
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Fig. 1
(a)
I
ZrO2 film II
II
Cr/CrN/Cr2O3 film III
III
Zr O Cr N
Intensity /Arb. units
(b)
Zr-4 alloy substrate I
0
5
10
15
20
Distance /m
9
25
30
Fig. 2 ■
(a)
■
Zr ▼ ZrO 2
Cr2O3 Cr
Intensity /a.u.
▼
■
▼ ▼
▼ ▼ ▼ ■
■
glancing angle
■
▼ ▼▼
▼
■ CrN
▼ ▼ ▼
▼ ▼
▼
▼
▼
-2 scan 20
20000
40
(b)
Counts /s
16000
12000
60
80
2Theta /()
Experiment Fitted curve Background Peak 1 Peak 2 Peak 3
Cr 2p3/2 CrN
Cr2O3
metallic Cr
8000
4000
582
580
578
576
574
572
Binding Energy /eV
10
570
Fig. 3
0.0
ZrO2+Cr/CrN/Cr2O3 film
2
-0.2 ZrO2+Cr/CrN/Cr2O3 film
-0.4
500
ZrO2 film
-0.6
ZrO2 film 1E-7
1E-6
1E-5
1E-4
Current density (A·cm
0
1E-3
-2
)
2
|Z| (Ω cm )
ZrO2+Cr/CrN/Cr2O3 film
1000 ZrO2 film
100
-2
0
10
2
10
10
4
10
6
10
Frequency (Hz) 60
(d)
50
30
peak 2
peak 1
40 ZrO2 film
20 10 ZrO2+Cr/CrN/Cr2O3 film
0 -10 -2 10
0
10
2
10
Frequency (Hz)
0
1000
2000
3000 2
Z' （Ω·cm ）
(c)
10000
Phase angel (degree)
(b)
1000
-Z" (Ω·cm )
Potential (V, SCE)
1500
(a)
0.2
4
10
6
10
11
4000
5000
Conflicts of interest None.
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Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Highlights 1. 2. 3. 4. 5.
A particular ZrO2 and Cr/CrN/Cr2O3 composite film was prepared. Cr2N was decomposed to CrN and Cr during the PLD process. The Cr/CrN/Cr2O3 film can seal the porous ZrO2 film surface. The composite film exhibits excellent corrosion resistance at high temperature. The corrosion current density of composite film is only 40% of single ZrO2.
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