Verification of the insulator coating concept for fusion blanket with self-healing capability

对于以液态锂为增殖剂/冷却剂、钒合金为结构材料的聚变包层，由于磁流体动力学（MHD）效应引起的流动锂的压降是一个关键问题。为了减轻这种影响，已知用绝缘陶瓷涂覆毯内部是有效的。涂层的关键要求之一是与锂的相容性。近年来的研究表明，Er_2O_3在锂中具有很好的高温稳定性，原位涂层法是一种很有吸引力的技术，因为它可以在零件制造后在复杂的表面上进行涂层，并且有可能在不拆卸零件的情况下修复涂层中的裂纹。本研究的目的是验证在钒合金表面原位包覆Er_2O_3具有自修复潜力的概念。采用密封钼坩埚，在500 ~ 700 ℃温度范围内研究了掺铒锂中预氧化钒合金基体上Er_2O_3涂层的形成和生长。结果表明，涂层形成并向饱和方向生长。形成的涂层在锂中具有显著高的稳定性。在V-4Cr-4 Ti预充氧的最佳条件下，形成了定向排列的Ti-O沉淀物网状结构<100>，这是为形成氧化物涂层而储备的氧。通过对预裂涂层的锂再暴露试验，证明了涂层的自修复能力。并对该结构的形成机理和动力学进行了分析。

For the fusion blanket using liquid lithium as breeder/coolant and vanadium alloys as structural materials, pressure drop of the flowing lithium due to MHD (Magneto-hydrodynamic) effects is a critical issue. For mitigating this effect, coating of the blanket interior with insulating ceramics is known to be effective. One of the critical requirements of the coating is the compatibility with lithium. Recent studies showed that Er_2O_3 is quite stable in lithium to high temperature.The in-situ coating method is a quite attractive technology because it will enable coating on complex surfaces after fabrication of components and have the potential to heal cracks in the coating without disassembling the component. The purpose of this study, is to verify the concept of in-situ coating of Er_2O_3 on vanadium alloys having potentiality for the self-healing. Using a sealed Mo crucible, the formation and growth of the Er_2O_3 coating on pre-oxidized vanadium alloy substrate in the Er doped lithium was investigated from 500 to 700C. The results showed the coating formed and grew towards saturation. The coating formed had significantly high stability in lithium. In the optimum condition for oxygen pre-charging to V-4Cr-4Ti a net-structure of Ti-O precipitates oriented to <100> directions was formed, which is the storage of oxygen reserved for formation of the oxide coating. By the re-exposure tests of the pre-cracked coatings to lithium, the self-healing capability was demonstrated. The mechanisms and kinetics for the formation of the structure were also analyzed.