High-temperature Oxidation and Failure Behavior of the Cr-coated Zr-1.5Sn-0.2Fe-0.1Cr Alloy in Nitrogen Environment

SONG Guanghao; ZHOU Teng; CAI Zhenbing; ZHAO Mingyan; LIANG Mingxuan; HU Jianhong; ZHANG Jicheng

doi:10.16490/j.cnki.issn.1001-3660.2025.24.011

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Surface Technology ›› 2025, Vol. 54 ›› Issue (24) : 138-148. DOI: 10.16490/j.cnki.issn.1001-3660.2025.24.011

Corrosion and Protection

High-temperature Oxidation and Failure Behavior of the Cr-coated Zr-1.5Sn-0.2Fe-0.1Cr Alloy in Nitrogen Environment

SONG Guanghao¹, ZHOU Teng^1,*, CAI Zhenbing², ZHAO Mingyan¹, LIANG Mingxuan¹, HU Jianhong¹, ZHANG Jicheng¹

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Abstract

Chromium coatings on zirconium alloys are widely explored to mitigate the high-temperature degradation of nuclear fuel cladding under severe reactor transient conditions, particularly in the course of the Loss-of-Coolant Accident (LOCA). Given that nitrogen is not only the most abundant gas in the atmosphere (accounting for about 78% of the air by volume) but also commonly present in nuclear reactor environments, its potential effects cannot be overlooked. To clarify the effects of different atmospheric environments (air/N₂) on the phase evolution, interfacial chemistry and oxidation kinetics of Cr-coated zirconium alloys at elevated temperatures and to provide experimental and theoretical support for the application of accident-tolerant fuel (ATF) coatings in nuclear reactors, the work aims to investigate the response of Cr-coated zirconium alloy to air versus N₂ atmospheres under identical thermal histories at 1 200 ℃. A homogeneous and adherent chromium coating with a thickness of approximately 15 μm was fabricated on a Zr-4 substrate by multi-arc ion plating. Then, the coated sample was subject to isothermal oxidation in a Setaram Setsys Evolution thermogravimetric analyzer (TGA) at 1 200 ℃, during which the mass change was continuously monitored with high precision to derive oxidation kinetic curves. The microstructures, chemical compositions and phase constituents of the samples before and after the oxidation exposure were characterized respectively by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results indicated that the Cr-coated zirconium alloy sample underwent oxidation in both air and nitrogen environments at 1 200 ℃, with chromium oxide (Cr₂O₃) forming as the oxidation product. Nevertheless, compared to the air environment, the Cr coating in the nitrogen atmosphere also underwent nitridation, forming a CrN layer. Significant differences were observed in the surface morphology and structure after oxidation: air exposure led to the development of granular aggregates uniformly distributed across the oxide scale, whereas N₂ treatment produced worm-like clusters and sinuous ridges. The results of the oxidation kinetics curves indicated that oxidation in air exhibited a rapid initial mass gain, which subsequently transitioned into a parabolic trend. In contrast, the overall mass gain in N₂ was lower (6.32% less than in air). Cross-sectional analysis further revealed distinctly different layered architectures dependent on the atmosphere. After oxidation in air, a well-defined three-layer structure was formed: (i) an outer Cr₂O₃ scale acting as the primary diffusion barrier; (ii) an intermediate layer of residual chromium; and (iii) an inner interdiffusion zone of Cr-Zr at the coating/substrate interface. In contrast, exposure to N₂ resulted in a seemingly simpler bilayer structure. The structure primarily consisted of an outer Cr₂O₃ scale and an inner residual Cr layer. However, combined XRD and EDS elemental analysis results confirmed the presence of a thin CrN interlayer between these two layers. As the reaction proceeded, the diffusion of nitrogen atoms into the zirconium substrate led to significant nitrogen enrichment adjacent to the interface, simultaneously creating a localized zone of oxygen depletion. This phenomenon was consistent with the formation of ZrN at the interface. The presence of nitride phases effectively suppressed the interdiffusion of Zr and Cr, thereby inhibiting the formation of Cr-Zr intermetallic compounds. Consequently, the high-temperature oxidation resistance of the Zr-4 alloy was significantly enhanced, which exerted a positive effect on the service performance of the Cr-coated zirconium alloy. In summary, the Cr coating significantly improves the oxidation resistance of the Zr-4 alloy. All the findings of this study provide critical insights for optimizing chromium coatings for accident-tolerant fuel cladding, thereby advancing their prospects for practical implementation.

Key words

ATF / Cr coating / Zr alloys / high-temperature oxidation failure / nitrogen atmosphere / diffusion

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SONG Guanghao, ZHOU Teng, CAI Zhenbing, ZHAO Mingyan, LIANG Mingxuan, HU Jianhong, ZHANG Jicheng. High-temperature Oxidation and Failure Behavior of the Cr-coated Zr-1.5Sn-0.2Fe-0.1Cr Alloy in Nitrogen Environment[J]. Surface Technology. 2025, 54(24): 138-148

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