To address the oxidation and corrosion challenges of zirconium alloy claddings in nuclear reactors under high-temperature steam environments, the work aims to employ in situ ceramicization technology to fabricate a composite ceramic coating, so as to enhance the high-temperature oxidation resistance, steam corrosion resistance, and accident tolerance performance (Accident Tolerant Fuel, ATF) of zirconium alloys. A hybrid fabrication process combining micro-arc oxidation (MAO) and atmospheric plasma spraying (APS) was developed to prepare the composite ceramic coating system, with particular emphasis on optimizing the microstructure of the MAO interlayer. The experimental protocol involved systematic screening of different MAO power supply modes, including unipolar pulse (UP), bipolar pulse (BP), and two-step pulse (TS), to regulate the microstructural evolution and compositional characteristics of the oxide layer. Subsequent APS deposition was performed to establish a multilayered protective architecture. Comprehensive material characterization techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were employed to analyze the morphological features, phase composition, and chemical states of the MAO-derived oxide layers. Mechanical integrity and environmental resistance were evaluated through scratch testing and high-temperature steam corrosion experiments, providing quantitative assessment of interfacial bonding strength and long-term durability. Experimental results demonstrate that the MAO base layer fabricated via the two-step pulse (TS) mode consists of a mixed phase of ZrO2 and Al0.52Zr0.48O1.74, forming a gradient dense structure that significantly reduces crack density. The coating prepared under the TS mode exhibits an interfacial bonding strength of 16 MPa, representing a 128% and 300% improvement compared to the unipolar pulse (UP, 7 MPa) and bipolar pulse (BP, 4 MPa) modes, respectively. High-temperature steam corrosion tests (1 200 ℃, 4 000 s) reveal that the 30 μm-thick coating shows the lowest oxidation weight gain rate and maintains structural integrity, while the 80 μm-thick coating experiences spallation due to accumulated thermal stress. Microstructural analysis reveals that the TS power mode facilitates controlled plasma discharge behavior during MAO process, promoting the formation of a gradient oxide structure with reduced microcrack density and improves phase stability. The mechanism underlying performance enhancement can be attributed to two synergistic effects. Firstly, the MAO-derived oxide layer acts as an effective diffusion barrier, suppressing oxygen penetration and hydrogen absorption at the substrate-coating interface. Secondly, the tailored surface morphology and chemical compatibility of the MAO interlayer create favorable conditions for APS coating adhesion through mechanical interlocking and chemical bonding. By precisely regulating the electrical parameters during MAO process, this study establishes a methodology for achieving optimal interfacial compatibility between the metallic substrate and ceramic coating system and provides critical insights into surface engineering strategies for nuclear-grade zirconium alloys. The developed composite coating architecture demonstrates threefold advantages of enhanced interfacial integrity through MAO layer optimization, superior environmental resistance via multilayered ceramic protection, and controllable thickness for maintaining neutron economy in reactor applications. The TS-mode MAO process proves particularly effective in balancing coating density and residual stress distribution, addressing the longstanding challenge of ceramic coating spallation under thermal cycling conditions. Further investigation should focus on long-term stability assessment under simulated loss-of-coolant accident (LOCA) scenarios and neutron irradiation effects. Nevertheless, the current findings establish a viable pathway for developing advanced ATF cladding materials through hybrid surface modification techniques, potentially extending the operational safety margins of nuclear reactors under both normal and accident conditions.
Key words
nuclear reactors /
zirconium alloy /
micro-arc oxidation /
atmospheric plasma spraying /
high-temperature oxidation
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Funding
The Innovation Team of Universities of Guangdong Province (2023KCXTD030); Open Project of Foshan Taoyuan Institute of Advanced Manufacturing (TYKF202203006)
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