P91钢在高流速液态铅铋介质中的冲蚀行为

Erosion–corrosion behaviors of P91 steel in high-velocity flowing lead–bismuth eutectic

基于第四代核能系统的发展和需求,铅冷快中子反应堆(Lead-cooled fast reactor,LFR)是下一步优先发展的6种主要堆型之一.铅冷快堆以液态纯铅(Lead)或铅铋共晶合金(Lead-bismuth eutectic,LBE)作为冷却剂,然而在高温、高流速条件下,LBE与结构材料的冲刷腐蚀磨损严重限制了其工程应用.本文以P91钢为研究对象,在相对流速为5 m·s^(−1),温度分别为350℃和450℃,不进行控氧处理的LBE中进行了3000 h的动态测试.研究发现,350℃时P91钢表面生成的氧化层为多层结构:从外到内分别为疏松的Fe_(3)O_(4)层、Fe–Cr尖晶石层、内氧化区(Internal oxidation zone,IOZ),合金表面氧化层经历了“生成—剥落—再生成”的动态平衡过程.当介质温度为450℃时,试样表面氧化腐蚀现象更加严重,但是不同冲击迎角区域的试样表面腐蚀特征有较大差异.试样表面损伤的严重程度排序为:30°>90°>−90°.30°迎角区域氧化层完全剥落,且LBE渗透入基体;90°迎角区域部分氧化层剥落,内部基体未受到LBE侵蚀;−90°迎角区域氧化层结构保持完整.本文分析了P91钢在高流速(5 m·s^(−1))LBE中的冲蚀行为,阐明了合金氧化层的生成和剥落机制,可以为我国第四代核反应堆LFR结构或包壳材料研发及其在LBE中腐蚀机制研究提供一定实验数据与参考.

Lead–bismuth eutectic(Pb–Bi)alloy,a liquid heavy metal,has garnered substantial attention as a candidate coolant for next-generation lead-cooled fast reactors(Gen-IV LFRs)and accelerator-driven systems(ADSs)owing to its exceptional nuclear and thermophysical properties.The demanding operational context within which these systems function poses significant challenges to the chemical and mechanical stability of traditional structural materials when in contact with lead–bismuth eutectic(LBE).Addressing the degradation and failure mechanisms of structural and fuel cladding materials in the presence of LBE is of paramount importance for the advancement and application of LFR and ADS technologies.Among various candidate materials,ferrite/martensite(F/M)steel has been considered an ideal candidate for LBE-cooled reactor fuel cladding owing to its excellent mechanical properties,high-temperature mechanical performance,radiation resistance,and lower coefficient of thermal expansion.This study focuses on P91 F/M steel.Dynamic tests were performed for up to 3000 h in uncontrolled oxygen LBE at a relative flow velocity of 5 m·s^(−1)and temperatures of 350℃and 450℃.The surface and cross-sectional corrosion morphologies of the alloy under different temperatures and exposure times were systematically analyzed by scanning electron microscopy.The composition and structural evolution of the oxide layer formed on P91 steel were summarized,and the mechanism of oxide layer spallation was proposed.In addition,electron backscatter diffraction was used to analyze the grain size,stress distribution,and proportion of large-angle grain boundaries in different impact angle regions between LBE and the samples,providing a detailed discussion of the erosion mechanism of the alloy in these regions.At 350℃,the oxide layer is a multilayer structure comprising a porous Fe_(3)O_(4)layer,Fe-Cr spinel layer,and inner oxidation zone undergoing a dynamic equilibrium process of“formation–spallation–reformation”.At 450℃,the oxidation-corrosion phenomenon is severe,with LBE penetration observed in addition to oxidation.The corrosion characteristics on the sample surface vary significantly across different impact angle regions.The severity of surface damage is ranked as follows:30°>90°>−90°.The oxide layer in the 30°angle region completely spalls,with LBE penetrating into the matrix.The 90°angle region shows spalling of the porous outer oxide layer,leaving only the inner oxide layer,with the inner matrix uneroded by LBE.The−90°angle region maintains an intact oxide layer structure that is free from LBE erosion.In this work,the corrosion–erosion behaviors of P91 steel in high-velocity(5 m·s^(−1))LBE are studied,the formation and spallation mechanisms of the oxide scales are elucidated,and the erosion damage mechanism of the alloy are revealed,providing experimental data and references for the development of structural or cladding materials for China’s fourth-generation nuclear reactors and the study of their corrosion mechanisms in LBE.