Ni基高温合金在LiCl-KCl熔盐中的腐蚀行为研究

Corrosion Behavior of Ni-Based Superalloys in LiCl-KCl Molten Salt

摘要:

熔盐电解精炼是乏燃料干法后处理的核心工艺单元，其反应容器需在高温、LiCl-KCl熔盐环境下长期服役，活泼合金元素Cr的选择性溶解使得钝化Cr₂O₃保护膜难以生成，结构材料面临严重的腐蚀问题，严重阻碍了干法后处理技术的工程化应用。Ni基高温合金在高温氯化物熔盐中的热力学性质稳定，是电解精炼反应容器潜在的候选材料，然而目前Mo、W等关键合金元素对Ni基高温合金在LiCl-KCl熔盐中的耐腐蚀性能影响暂不明确。采用浸泡腐蚀的方法，研究了Haynes 230、Inconel 625、GH 3535、Inconel 690和GH 4169五种Ni基高温合金在550 ℃、氩气气氛下LiCl-KCl熔盐中的腐蚀行为，采用X射线衍射、扫描电子显微镜及能谱分析对腐蚀产物的组成和形貌进行了分析。研究结果表明，五种Ni基高温合金在与LiCl-KCl熔盐相互作用的过程中均发生腐蚀失重，失重情况为Inconel 625＞GH 3535＞Haynes 230＞Inconel 690＞GH 4169。其中Inconel 625和GH 4169合金在基体近表层生成了富Mo氧化膜，导致外层(Cr,Fe)₂O₃与基体的热相容性变差，有明显的脱落趋势。相比高Cr含量的Inconel 690合金发生严重的电化学溶解，低Cr的GH 3535合金外层(Cr,Fe)₂O₃含量低，抗氧化能力也明显降低，使得氧向基体内部渗入。而Haynes 230合金外表面生成了富W的氧化物，有效地阻挡了Cl^-的侵蚀，在以上五种Ni基高温合金中具有最好的耐腐蚀性能。

Abstract:

Molten salt electrorefining is the core process unit of spent nuclear fuel dry post-processing， and its reaction vessel needs to be used for a long time in a high-temperature， LiCl-KCl molten salt environment. The selective dissolution of the active alloying element Cr makes it difficult to form a passivation Cr₂O₃ protective film， and the structural material faces serious corrosion problems， which seriously hinders the engineering application of dry post-treatment technology.so the structural materials face serious corrosion problems. Ni-based superalloys have stable thermodynamic properties in high-temperature chloride molten salts and are potential candidate materials for electrolytic refining reaction vessels.Ni-based superalloys are potential candidates for electrorefining reaction vessels. But the effect of key alloying elements such as Mo and W on the corrosion resistance of Ni-based superalloys in LiCl-KCl molten salt is not clear. The corrosion behavior of five Ni-based superalloys， Haynes 230， Inconel 625， GH 3535， Inconel 690 and GH 4169， in LiCl-KCl molten salt at 550 ℃ under argon atmosphere was studied by immersion corrosion. The composition and morphology of the corrosion products were analyzed by X-ray diffraction， scanning electron microscopy and energy spectrum analysis. The results show that the corrosion loss of the five Ni-based superalloys is Inconel 625>GH 3535>Haynes 230>Inconel 690>GH 4169. Inconel 625 and GH 4169 alloys have a Mo-rich oxide film on the near surface of the matrix， resulting in poor thermal compatibility between the outer （Cr，Fe）₂O₃ and the matrix. Compared with Inconel 690 alloy， GH 3535 alloy with low Cr content inhibits the selective dissolution of Cr element， but also reduces the oxidation resistance. Haynes 230 alloy has the best corrosion resistance among the five Ni-based superalloys with W-rich oxides formed on the outer surface， which effectively blocks the erosion of Cl^-.