目的 探究CLF-1钢在不同氧化条件下预处理后,其预氧化层结构与氢同位素渗透行为的关联及作用机制,并以此抑制氢同位素在CLF-1钢中的渗透。方法 通过调控氧化气氛、温度和时间,对CLF-1钢进行预氧化处理,采用X射线衍射仪（XRD）、场发射扫描电子显微镜（SEM）和能谱仪（EDS）表征预氧化层物相组成、微观结构与元素分布,采用高温气相驱动渗透平台开展氘渗透试验,分析氢同位素的渗透行为。结果 在富氧条件下,氧化温度为400~700 ℃时,表面主要生成Cr2O3层;700 ℃保温2 h样品的PRF最高为5,渗透激活能升至42.55 kJ/mol;氧化温度为800 ℃时,表面为Fe氧化物层,并出现大量开裂与剥落。在微量氧条件下,表面为Fe3O4/FeCr2O4复合氧化层,呈外层富Fe、内层富Cr结构,800 ℃保温24 h样品的PRF最高为11,指前因子骤降,渗透激活能降至17.75 kJ/mol。结论 富氧、中低温（400~700 ℃）条件下形成的Cr2O3层通过增加扩散能垒抑制氢同位素的扩散,微量氧条件下生成的Fe3O4/FeCr2O4复合氧化层,能够通过氧化层和其内部少数微观缺陷的综合作用表现出对氘渗透的抑制,其中800 ℃保温24 h条件下生成的氧化层对氘渗透的抑制效果最优。
Abstract
Reduced activation ferritic/martensitic (RAFM) steels, such as the CLF-1 steel developed by China, are primary candidate structural materials for the tritium breeding blankets of future nuclear fusion reactors. However, their inherent high hydrogen isotope permeability and significant tritium retention pose critical challenges to fuel self-sufficiency and radiological safety. While dedicated barrier coatings are highly effective, tailored pre-oxidation treatment presents a viable, cost-effective, and procedurally simple synergistic protective strategy that offers excellent thermodynamic compatibility, especially for complex internal components. Furthermore, during actual reactor operation, components are exposed to extremely low oxygen partial pressures rather than ambient air. Therefore, the work aims to systematically investigate the microstructural evolution and deuterium permeation behavior of pre-oxidation layers formed on CLF-1 steel under both oxygen-rich and simulated low oxygen potential environments, so as to elucidate the underlying mitigation mechanisms.
CLF-1 steel samples were subjected to varied pre-oxidation treatments at temperatures ranging from 400 to 800 ℃ for durations of 2, 10, and 24 hours under atmospheric air and argon environments. The phase compositions, surface and cross-sectional microstructures, and elemental distributions of the resultant oxide films were extensively characterized through X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Subsequently, macroscopic deuterium permeation kinetics were evaluated with a high-temperature gas-driven permeation platform at testing temperatures of 400-500 ℃. Key kinetic parameters, including the permeation reduction factor, permeation activation energy, and the pre-exponential factor, were quantitatively derived to assess the inhibition efficacy.
The structural architecture and subsequent permeation inhibition efficacy of the pre-oxidation layers were jointly dictated by the oxygen partial pressure and the oxidation temperature. Under oxygen-rich conditions at moderate temperatures (400-700 ℃), a continuous and dense Cr2O3 protective layer preferentially formed. The optimal sample synthesized at 700 ℃ for 2 hours achieved a maximum PRF of 5, accompanied by an increase in the permeation activation energy from 36.37 kJ/mol (bare substrate) to 42.55 kJ/mol, confirming that the dense Cr2O3 lattice introduced an additional energy barrier that effectively impeded the bulk diffusion of deuterium atoms. Conversely, when the oxidation temperature reached 800 ℃ in air, the high mobility of Fe cations in the oxide lattice and the absolute concentration advantage of Fe in the substrate led to the rapid dominant growth of Fe-based oxides. The substantial mismatch in the Pilling-Bedworth ratio between the iron oxides and the substrate, coupled with accumulated thermal stresses during cooling, induced severe multi-layer transverse cracking and massive spalling, rendering the layer entirely ineffective as a permeation barrier.
Under trace oxygen conditions simulated by high-purity argon, the severely restricted oxygen flux fundamentally altered the oxidation kinetics. At lower temperatures, the insufficient lateral growth of initial oxide and the rapid outward diffusion of Fe cations resulted in significant vacancy coalescence, producing highly porous layers. However, at 800 ℃, the increase in Cr bulk diffusion facilitated the formation of a robust double-layer architecture comprising an outer Fe-rich passivation layer (Fe3O4) and an inner Cr-rich spinel layer (FeCr2O4) with a thickness of approximately 20 μm after 24 hours. Remarkably, the sample annealed at 800 ℃ for 2 h exhibited superior barrier performance, yielding a PRF of 11. Moreover, macroscopic kinetic analyses revealed a drastic plunge in the pre-exponential factor and a sharp decrease in the activation energy to 17.75 kJ/mol.
Pre-oxidation treatments significantly alter the surface chemistry and hydrogen isotope permeability of CLF-1 steel. While moderate-temperature air oxidation mitigates permeation by elevating the bulk diffusion barrier via a Cr2O3 film, high-temperature oxidation under low oxygen partial pressures realizes enhanced inhibition by the combined effect of a tiny number of internal microscopic and the Fe3O4/FeCr2O4 composite layer defects inhibits deuterium penetration. This work establishes a mechanistic framework for the microstructural evolution of RAFM steels under diverse oxygen potentials and validates the engineering applicability of tailored pre-oxidation as an effective tritium permeation barrier strategy for fusion reactor components.
关键词
CLF-1钢 /
预氧化层 /
氢同位素 /
氘渗透 /
微观结构 /
渗透降低因子
Key words
CLF-1 steel /
pre-oxidation layer /
hydrogen isotope /
deuterium permeation /
microstructure /
permeation reduction factor
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基金
四川省自然科学基金青年项目（2024NSFSC1336）
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