| LI Zhi-ping,SONG Peng,ZHANG Rui-qian,LI Qing.High-temperature Air Oxidation/Diffusion Behavior of Cr-coated Zr-4 Alloy Cladding[J],52(9):241-246, 264 |
| High-temperature Air Oxidation/Diffusion Behavior of Cr-coated Zr-4 Alloy Cladding |
| Received:August 04, 2022 Revised:January 17, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.020 |
| KeyWord:multi-arc ion plating Cr coating Zr-4 alloy oxidation resistance diffusion |
| Author | Institution |
| LI Zhi-ping |
Key Laboratory of Reactor Fuel and Materials, Nuclear Power Institute of China, Chengdu , China |
| SONG Peng |
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming , China |
| ZHANG Rui-qian |
Key Laboratory of Reactor Fuel and Materials, Nuclear Power Institute of China, Chengdu , China |
| LI Qing |
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming , China |
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| Abstract: |
| After the Fukushima nuclear power plant accident in 2011, accident tolerant fuel (ATF) materials become the focus of international research to cope with loss of the coolant accidents (LOCA) and more severe accidents in the nuclear industry. Zr alloys are widely used as fuel cladding structural materials because of their low thermal neutron cross section coefficient, good oxidation resistance, good mechanical properties and high corrosion resistance. Protective coatings are an effective way to increase the emergency response time in an accident. Cr coatings are one of the most promising ATF coatings because of their excellent oxidation resistance, high-temperature stability, and good deformation compatibility with Zr alloys in high-temperature environment. Cr coating was prepared on the surface of Zr alloy cladding by multi-arc ion plating technology to improve the high-temperature oxidation resistance of Zr alloy fuel cladding under accident environment. The high-temperature oxidation performance of the samples was evaluated at 1 100, 1 200 and 1 300 ℃ in an air environment. The microstructure of as-deposited Cr coatings was dense and homogeneous, with a strong texture on the (110) planes. No microcracks or voids were found on the coating surface and cross section, and the Cr coating had a uniform thickness of about 17 μm. The Cr coatings maintained the structural integrity after oxidation in air at 1 100, 1 200 and 1 300 ℃ for 60 min. The oxidation products of all Cr coatings were identified as Cr2O3. The relative strength of Cr (110) peak decreased with the increase of oxidation temperature. However, the relative strength of Cr2O3 (110) peak increased. The oxidized Cr-coated Zr alloy system was multi-layer:external Cr2O3 layer, intermediate Cr coating, internal Cr-Zr diffusion layer, and Zr alloy substrate. No microvoids, cracks or spalling were found on the surface of the dense Cr2O3 layer, but mound oxide layer was formed on the specimen surface. Considering that the PBR of Cr2O3 was 2.07, the strong volume expansion during high-temperature exposure led to an increase in compressive stress of the coating. Then, a large difference in the thermal expansion coefficients of Cr2O3 (9.6×10–6 /K) and Cr (6.5×10–6 /K) led to the formation of cracks or voids at the interface between the Cr coating and the Cr2O3 layer during cooling. Due to the inhomogeneous diffusion rate, the Cr/ZrCr2/Zr-4 interface became significantly rough. An intermetallic ZrCr2 diffusion layer with Laves phase was formed at the coating/substrate interface, and a large number of dispersed precipitates appeared in the region below the ZrCr2 layer. The solid-state reaction between Cr and Zr diffusion at high temperature led to the formation of the ZrCr2 diffusion layer. The asymmetric atomic diffusion at the interface between the Cr-Zr interlayer and the Zr alloy led to the formation of Kirkendall vacancies, and the aggregation and coalescence of vacancies led to the nucleation and growth of voids. A dense Cr2O3 layer on the surface of the Cr coating improves the high-temperature oxidation resistance of the Zr-4 alloy. The study on the oxidation/diffusion behavior of Cr coated Zr-4 alloy cladding materials in high-temperature air can provide theoretical guidance and technical support for the development, preparation and application of accident tolerant coatings. |
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