含铝奥氏体耐热钢在超临界二氧化碳中的腐蚀行为

研究了20Cr-25Ni合金和一种新型结构材料含铝的奥氏体耐热钢(AFA钢)在600℃/20 MPa的超临界二氧化碳(S-CO₂)环境中的腐蚀行为,并对2种合金的氧化膜形貌、成分和结构进行分析。研究发现,20Cr-25Ni合金出现明显的腐蚀增重增长趋势,表现出“抛物线”上升规律;AFA钢腐蚀增重趋势缓慢,腐蚀1000 h后仅为2.11 mg/dm²。20Cr-25Ni合金表面出现粗大的氧化产物,随腐蚀时间延长,AFA钢的氧化膜始终保持致密、连续。通过氧化膜的截面形貌分析发现,20Cr-25Ni合金腐蚀后具有两层氧化膜结构,主要由Fe₃O₄和FeCr₂O4_氧化层以及少量尖晶石组成。而AFA钢中出现了3层氧化膜结构,中间和最内层分别为Cr₂O₃和Al₂O₃氧化膜,最外层分布了一层不连续的FeCr₂O₄尖晶石氧化物。由于形成了致密的...     

SPD技术对锆及锆合金力学行为影响研究现状

综述了锆及锆合金剧烈塑性变形(SPD)后性能变化的研究进展,系统阐述了锆及锆合金经剧烈塑性变形后显微硬度、拉伸/压缩性能、高低周疲劳性能,重点介绍了SPD技术在纯锆、Zr-Nb系合金中的应用.经过剧烈塑性变形后,锆及锆合金的抗拉强度及屈服强度均显著提升,但依据剧烈塑性成形轨迹、合金成分、第二相分布、热处理制度不同,其提...     

反应堆乏燃料贮运用中子吸收材料的研究进展

从我国对乏燃料贮运用中子吸收材料的需求出发,简述了乏燃料贮运用中子吸收材料的特点、国内外研究及应用现状。重点阐述了含硼不锈钢、B4C/Al、硼铝合金、含硼有机聚合物4种含硼中子吸收材料的制备工艺、性能以及存在的问题,同时对目前我国使用的不锈钢包覆金属镉中子吸收材料和国外正在研究的含钆合金中子吸收材料进行了概述。提出了B4C/Al和硼钢两种中子吸收材料应作为进一步研究的重点。     

Mechanical and optical property assessment of irradiated SiC with displaced atoms

Explicit method to emulate neutron radiation effects on key ceramic materials is lacking, with most literatures stressing direct comparison between radiation parameters while underestimating the defect-property correlation. Herein, the evolutionary correlation between defects of displaced atoms and properties in 6H-SiC was systematically investigated, aiming to found the basis for performance assessment of neutron irradiated material. The point defect accumulation, defect cluster growth, and homogeneous crystalline-amorphous (c-a) transition were recognized, with different stages of Young’s modulus reduction and optical absorption enhancement accordingly triggered. Specifically, the relaxation process accompanying the c-a transition was believed to induce the final reduction stage of Young’s modulus and account for the conflict between existing research results. Average lattice disorder, regarded as the average density of displaced atoms, was proved to be the success reference in the property assessment approach, paving the way for the extension into high temperature radiation where more defect types coexist.     

Influence of thermal effect on dislocation loop evolution in Fe+-irradiated CeO2 during in-situ annealing

Cerium dioxide (CeO₂) is widely used as a surrogate fuel for uranium dioxide (UO₂) because of their same cubic fluorite crystal structure, nearly identical lattice parameters and similar physical properties. The degree of irradiation damage is related not only to the irradiation dose but also to the thermal effect. The influence of the thermal effect on the microstructure of Fe⁺-irradiated CeO₂ was investigated using in-situ transmission electron microscopy analysis during annealing. Shrinkage of the dislocation loops was observed for the first time in the irradiated CeO₂ foil. The threshold size determining whether the dislocation loop shrank was found to be approximately 19 nm through experimental measurements. When the loop size was less than this value, the dislocation loop shrank or even disappeared as the annealing time increased. Moreover, the smaller the loop size, the larger the shrinkage. The shrinkage rate measured in the in-situ annealing experiment was approximately 0.08 nm/s, which was almost consistent with the theoretical calculation (about 0.11 nm/s). However, when the loop size was larger than 19 nm, the loop grew rapidly at the beginning of annealing and then remained stable.     

In Steam Short-Time Oxidation Kinetics of FeCrAl Alloys

In order to investigate the oxidation process of FeCrAl alloy developed by NPIC under simulated LOCA conditions, three experimental groups of alloys were exposed to the steam atmosphere and heated to test temperature (550, 1000, and 1200 °C), respectively, and then maintained at the temperature for 4 hours. The oxidation kinetics of alloys were obtained with a high-precision synchronous thermal analyzer, and the oxide film was investigated by XPS, XRD, and SEM technologies. The results showed that the FeCrAl alloy still retains good oxidation resistance under 1200 °C steam atmosphere. The oxidation process of alloy at 1200 °C can be described into six stages.     

Structural evolution and mechanical properties of Cansas-III SiC fibers after thermal treatment up to 1700 °C

The effects of thermal treatment on the Cansas-Ⅲ SiC fibers were investigated via heating at temperatures from 900 to 1700 ℃ for 1–5 h in argon atmosphere. The composition and morphology of the SiC fibers were characterized and the tensile strength of the SiC fiber bundles was analyzed via two-parameter Weibull distribution analysis. The results showed that the thermal treatment has negligible influence on the microstructure of the SiC fibers at temperatures ≤ 1100 ℃. At temperatures ≥ 1300 ℃, the surface of the fibers became rough with some visible particles. Particularly, at 1700 °C, numbers of holes appeared. With the increasing of heating temperature and holding time, the average tensile strength of the SiC fibers decreased gradually from 1.81 to 1.01 GPa. The decreasing of tensile strength can be attributed to the increase of critical defect sizes, grain growth and phase transformation (β→α) of SiC.     

Influence of Cold-Rolling Reduction on Microstructure and Tensile Properties of Nuclear FeCrAl Alloy with Low Cr and Nb Contents

FeCrAl alloy is one of the most promising candidates as an accident-tolerant fuel (ATF) cladding material. Herein, the influence of cold-rolling (CR) reduction on microstructure and tensile properties of the as-annealed FeCrAl alloys, with low Cr and Nb contents, is systematically examined. With the increase in CR reduction, the grain size of FeCrAl alloy is obviously refined after annealing because the increase in stored deformation energy leads to enhanced recrystallization. However, the large CR reductions result in a severe mixed-grain microstructure, significantly reducing the uniform deformability of the FeCrAl alloy. The dislocation density of the as-annealed FeCrAl alloy decreases with the increase in CR reduction, except for the excessive CR reduction of 50%. Moreover, the Laves phases are crushed and dissolved during CR and annealing, as well as large amounts of refined Laves phases are found after large CR reductions. The pinning effect of the Laves phases can significantly improve the strength of FeCrAl alloy. Accordingly, the strengthening mechanisms of FeCrAl alloy consist of fine-grain strengthening, dislocation strengthening and precipitation strengthening. Finally, the FeCrAl alloy, with a CR reduction of 30%, achieves optimal tensile properties. This study can provide theoretical guidance for the industrial production of the FeCrAl alloy.     

Microstructure response of Amosic-3 SiC/SiC composites under self-ion irradiation

Amosic-3 SiC/SiC composites were irradiated at 300 °C using 6 MeV Si ions to peak doses of 13 and 55 displacements per atom (dpa). The loss of amorphous carbon packets and the growth of SiC grains were simultaneously observed in Amosic-3 SiC fibers, using a combination of transmission electron microscopy (TEM) and Raman spectroscopy. A mechanism based on the grain growth theory was proposed to expound the relationship between the loss of carbon packets and the growth of SiC grains. Small and curved SiC grains can absorb surrounding carbon packets to grow themselves; at some point, these grains further grow at the expense of adjacent small SiC grains until their grain boundary became straight. TEM images were found to support the above mechanism.     

Molecular dynamics studies of hydrogen diffusion in tungsten at elevated temperature: Concentration dependence and defect effects

Influence of hydrogen concentration and defects introduced by neutron irradiation on hydrogen diffusion in tungsten has been investigated by molecular dynamics simulation at elevated temperatures. Hydrogen diffusion is shown to be significantly restrained at high concentrations due to spontaneous formation of platelet-like hydrogen clusters. For neutron irradiation defects, self-interstitials, mono-vacancies and vacancy clusters are considered. By clustering and acting as dislocation loops, self-interstitials show considerable trapping effects on hydrogen, leading to the suppression of hydrogen effective diffusion and the change of diffusion model in which hydrogen mainly diffuses along dislocation lines instead of hopping between tetrahedral interstitial sites. Moreover, an equation connecting hydrogen diffusion parameters and the total length of dislocation loops is empirically established. Different influences of mono-vacancies and vacancy clusters on hydrogen diffusion have been carefully identified. With the same vacancy concentration, hydrogen diffusivity is lower with mono-vacancies than that with vacancy clusters because more isolated trapping sites are provided by mono-vacancies. This work is not only helpful for understanding the synergistic effects of neutron irradiation and plasma interaction, but also potentially applicable for larger scale simulations as input data.