目的 探究稀土掺杂对Fe-Al/Al2O3复合涂层的微观特征、氧化动力学以及相变过程的影响,提升阻氚性能。方法 采用包埋渗铝法在基体上分别沉积稀土改性与未经稀土改性的Fe-Al涂层,随后原位氧化制备了Fe-Al/Al2O3复合涂层。开展热重分析实验,通过掠入射X射线衍射（GIXRD）和扫描电子显微镜（SEM）分析观察氧化铝涂层结构和组织形貌在工艺温度下的演变规律。结果 经稀土改性的Fe-Al/Al2O3复合涂层与基体结合良好,未出现孔洞和裂纹,Fe-Al层厚度约为17.0 μm,氧化膜厚度约为200 nm;未经改性的涂层则出现明显裂纹,Fe-Al层厚度约为12.8 μm。氧化动力学曲线表明,稀土改性Fe-Al层存在2个氧化阶段,Ⅰ阶段的氧化速率为3.78×10-14 g2/(cm4∙s),Ⅱ阶段的氧化速率为2.72×10-15 g2/(cm4∙s),二者均高于未经稀土改性Fe-Al层的氧化速率2.18×10-15 g2/(cm4∙s)。改性样品经约180 min氧化后,氧化膜内开始形成α-Al2O3相;当氧化时间延长至4 h,γ-Al2O3相已完全转化为单一α-Al2O3相。未改性样品氧化膜在同等氧化条件下,始终维持单一的γ-Al2O3相,未发生γ至α的相转变。结论 稀土元素掺杂能够优化涂层与基体的结合特性,通过动态偏析、缺陷结构优化、电子态调制等机制协同提高Fe-Al层表面Al2O3的生长速率,在较低温条件下促进Al2O3发生相变,增加α-Al2O3相的比例,提高涂层阻氚性能。
Abstract
The Fe-Al/Al2O3 composite coating has been established as a preferential TPB (Tritium Permeation Barrier) for structural materials of fusion reactors, with α-Al2O3 demonstrating superior hydrogen permeation resistance. To optimize coating performance and elevate α-Al2O3 content, rare earth-modified coatings have become a key research priority in international studies. This work systematically examines the effects of rare earth elements on γ-α phase transformation in Al2O3 during the oxidation of Fe-Al layers, while evaluating their effects on microstructure evolution, oxidation kinetics, and phase composition in Fe-Al/Al2O3 composite coatings. Specimens are prepared through pack cementation deposition followed by in-situ oxidation, with comparative analysis conducted between rare earth-modified and unmodified coatings.
Thermogravimetric analysis (TGA) is employed to monitor structural and morphological changes in alumina coatings under elevated temperature. Phase identification and surface characterization are performed by glancing incident X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). The oxidation kinetics are quantified through mass gain measurements, revealing significant differences between modified and unmodified systems.
The rare earth-modified Fe-Al/Al2O3 coating exhibits excellent substrate adhesion with no detectable pores or cracks through microscopic examination. Cross-sectional analysis reveals a 17.03 μm thick Fe-Al interlayer and an approximately 200 nm oxide scale. In contrast, the unmodified coating displays extensive cracking with a reduced Fe-Al layer thickness of 12.81 μm. Enhanced interdiffusion of Fe and Al is observed in the modified system, which is attributed to rare earth-induced acceleration of cation migration rates. This diffusion enhancement effectively minimizes interfacial voids and improves morphological stability during high-temperature exposure.
Kinetic analysis reveals two distinct oxidation stages in the rare earth-modified system. The initial stage (Stage Ⅰ) is characterized by rapid γ-Al2O3 formation, exhibiting an oxidation rate of 3.78×10-14 g2/(cm4∙s). This is followed by a stable growth phase (Stage Ⅱ) dominated by α-Al2O3 development, with a reduced rate of 2.72×10-15 g2/(cm4∙s). Both stages demonstrate significantly enhanced oxidation rates compared with the unmodified coating's single-phase behavior of 2.18× 10-15 g2/(cm4∙s). The accelerated kinetics are attributed to solute drag effects induced by rare earth elements during oxide scale formation. The modified system's dual-stage behavior contrasts with the unmodified coating's persistent γ-phase dominance, highlighting the critical role of rare earth additives in altering both reaction kinetics and phase evolution pathways.
Phase evolution studies reveal critical differences in alumina transformation pathways. In modified coatings, α-Al2O3 nucleation is detected after 3 hours of oxidation, with complete γ-α transformation achieved within 4 hours. Conversely, unmodified coatings retain pure γ-Al2O3 phases throughout the 4-hour oxidation period. This disparity is ascribed to rare earth elements acting as heterogeneous nucleation sites, effectively reducing the activation energy barrier for α-phase formation.
In summary, the incorporation of rare earth elements is demonstrated to significantly enhance coating performance. Improved bonding between the coating and the substrate is achieved through interdiffusion optimization. An accelerated growth rate of Al2O3 on Fe-Al layers is observed, which is attributed to rare earth-induced solute drag effects. The γ-α phase transformation is facilitated at reduced temperature, resulting in an increased α-Al2O3 phase fraction after 4 hours of oxidation. It can be inferred that the tritium resistance of the composite coating will be greatly improved then.
关键词
稀土改性 /
Fe-Al/Al2O3复合涂层 /
阻氚涂层 /
α-Al2O3 /
氧化动力学 /
相变过程
Key words
rare earth modification /
Fe-Al/Al2O3 composite coating /
tritium permeation barrier /
α-Al2O3 /
oxidation kinetics /
phase transformation
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