【作者】 王优；

【导师】 周张健；

【作者基本信息】 北京科技大学 ， 材料科学与工程， 2024， 博士

【摘要】 本研究旨在设计研发一种面向先进四代堆的新型燃料包壳候选材料,探索新型含硅纳米氧化物弥散强化(ODS)钢在先进第四代核反应堆更高温度和更强腐蚀环境下的应用潜力。本研究以12Cr-ODS钢为基础,通过粉末冶金法成功制备了不同硅含量的ODS钢,研究了硅元素对其显微结构、力学性能及其在液态铅铋(LBE)和超临界二氧化碳(S-CO2)两种典型冷却介质中的耐腐蚀性能的影响。实验采用多种先进的表征技术,如透射电子显微镜(TEM)、三维原子探针(3D-APT)、能量色散X射线光谱(EDX)、透射菊池衍射(TKD)、小角度掠入射X射线衍射(GIXRD)等,对所制备材料进行了全面的微观组织结构、力学性能、抗腐蚀性能等分析。实验结果显示,随着Si含量的增加,ODS钢的晶粒尺寸得以细化。并且其中析出了高数密度的超细Y-Si-O颗粒,随着Si含量增加,弥散氧化物颗粒的数密度提高、平均粒径减小。新型含硅ODS钢的细晶作用和晶粒内部大量弥散颗粒带来的弥散强化作用有助于提高材料的室温力学性能和高温力学性能。在室温、600℃和700℃下,材料的拉伸强度和屈服强度均随Si元素的添加量增加而提高。特别地,在高温下,新型含硅ODS钢的塑性未随强度提高而降低,具有优异的强塑匹配性。同时本研究设计制备的新型含硅ODS钢具有优异的抗高温腐蚀性能。一方面,在650℃、含10-6 wt.%溶解氧的高温LBE环境中,通过对比不同Si含量ODS钢经不同腐蚀时间后表面的溶解腐蚀和氧化腐蚀形貌可以发现,含硅ODS钢在250 h的腐蚀后已经在局部表面形成了具有保护性的多层氧化膜,而不含硅ODS钢在1000 h的腐蚀后仍未形成连续氧化膜。Si元素促进了 ODS钢在LBE中氧化膜的形成,保护材料表面减缓了高温LBE的溶解腐蚀。进一步地,新型含硅ODS钢在内层氧化层中形成了SiO2氧化膜,明显降低基体主要元素的快速外扩散速度,可避免内层氧化层中大量空位聚集导致的高密度孔洞的形成,从而提高了内层氧化层的致密性,降低了新型含硅ODS钢在高温LBE中长时间服役后氧化膜剥落的潜在风险。另一方面,新型含硅ODS钢在650℃、20 MPa的S-CO2环境中也展现出了优异的耐腐蚀性能,尤其在抗S-CO2的碳化腐蚀方面具有显著优势。新型含硅ODS钢通过在氧化膜中形成SiC的方式,一方面阻止了C的持续内扩散;另一方面避免了形成富Cr碳化物对Cr元素的消耗,加速连续致密Cr2O3氧化膜的形成,从而提高材料的抗S-CO2腐蚀性能。进一步地,当对新型含硅ODS钢进行表面磨光处理后,Si元素通过溶质拖拽效应向晶界偏析。Si沿晶界快速外扩散,在材料表面形成连续、致密、超薄的SiO2氧化膜,完全阻止C的内扩散,显著提高了新型含硅ODS钢在S-CO2中长时间的抗腐蚀性能。本研究通过对比不同硅含量ODS钢的腐蚀行为,揭示了硅元素在提高材料抗高温LBE腐蚀和S-CO2腐蚀中的关键作用和机理。论文结果为ODS钢在先进四代堆中的应用提供了重要的科学依据和理论基础。不仅为先进第四代核反应堆燃料包壳材料的开发提供了新的思路,也对未来高温、强腐蚀环境下材料的设计和制备具有重要的参考价值,推动了材料科学与核能工程领域的交叉融合与发展。更多还原

【Abstract】 This study aims to design and develop a new type of fuel cladding candidate material for advanced fourth-generation reactors,exploring the application potential of new siliconcontaining oxide dispersion strengthened(ODS)steel under higher temperature and more severe corrosion environments in advanced fourth-generation nuclear reactors.Based on 12CrODS steel,this study successfully prepared ODS steel with different silicon contents through powder metallurgy,investigated the effects of silicon on its microstructure,mechanical properties,and corrosion resistance in two typical coolant media:liquid lead-bismuth(LBE)and supercritical carbon dioxide(S-CO2).Various advanced characterization techniques were utilized,such as transmission electron microscopy(TEM),energy-dispersive X-ray spectroscopy(EDX),transmission Kikuchi diffraction(TKD),and grazing-incidence smallangle X-ray scattering(GIXRD),to comprehensively analyze the materials’ microstructural organization,mechanical properties,and corrosion resistance.Experimental results show that with the increase in Si content,the grain size of ODS steel was refined,and a high number density of Y-Si-O particles precipitated.With the increase in Si content,the number density of dispersed oxide particles increased,and the average particle size decreased.The fine grain effect and the dispersion strengthening effect brought about by a large number of dispersed particles inside the grains of the new silicon-containing ODS steel helped to improve the materials room temperature mechanical properties and high-temperature mechanical properties.At room temperature,600 ℃,and 700 ℃,the tensile strength and yield strength of the material increased with the addition of Si.Notably,at high temperatures,the plasticity of the new silicon-containing ODS steel did not decrease with the increase in strength,demonstrating excellent strength-plasticity matching.Furthermore,the newly designed silicon-containing ODS steel exhibited excellent hightemperature corrosion resistance.On one hand,at 650℃ in a high-temperature LBE environment containing 10-6 wt.%dissolved oxygen,comparing the surface dissolution corrosion and oxidation corrosion morphologies of different Si content ODS steel after different corrosion times revealed that silicon-containing ODS steel had formed a protective multilayer oxide film on the local surface after 250 hours of corrosion,while silicon-free ODS steel had not formed a continuous oxide film after 1000 hours of corrosion.Si element promoted the formation of an oxide film on ODS steel in LBE,protecting the material surface and slowing down the dissolution corrosion of high-temperature LBE.Furthermore,the new siliconcontaining ODS steel formed a SiO2 oxide film within the inner oxide layer,reducing the rapid outward diffusion speed of the matrix’s main elements,to prevent the formation of high-density pores caused by a large number of vacancies in the inner oxide layer,thereby improving the density of the inner oxide layer,and reducing the risk of oxide film peeling in high-temperature LBE after long-term service.On the other hand,the new silicon-containing ODS steel also exhibited excellent corrosion resistance in the S-CO2 environment at 650℃ and 20 MPa,especially showing significant advantages in resisting S-CO2’s carburization corrosion.The new silicon-containing ODS steel prevented continuous inward diffusion of C by forming SiC within the oxide film and avoided the consumption of Cr elements by forming rich Cr carbides,accelerating the formation of a continuous dense Cr2O3 oxide film,thereby enhancing the material’s S-CO2 corrosion resistance.Furthermore,after surface polishing of the new silicon-containing ODS steel,Si elements segregated to grain boundaries through solute drag effects.Si rapidly diffused along grain boundaries,forming a continuous,dense,thin SiO2 oxide film on the material’s surface,completely preventing inward diffusion of C,significantly improving the new siliconcontaining ODS steel’s long-term corrosion resistance in S-CO2.By comparing the corrosion behavior of ODS steel with different silicon contents,this study revealed the key role and mechanism of silicon in improving the material’s resistance to high-temperature LBE and S-CO2 corrosion.The results provide important scientific evidence and theoretical basis for the application of ODS steel in advanced fourth-generation reactors.It not only offers new ideas for the development of fuel cladding materials for advanced fourthgeneration nuclear reactors but also has significant reference value for the design and preparation of materials in high-temperature,high-corrosion environments in the future,promoting the interdisciplinary integration and development of material science and nuclear engineering.更多还原