超临界二氧化碳环境中600合金和304不锈钢的均匀腐蚀行为研究

为遴选可用于超临界二氧化碳核反应堆的结构材料,通过实验研究了应用于传统核反应堆中的两种合金（600合金和304不锈钢）在650℃、20 MPa的超临界二氧化碳环境中的均匀腐蚀行为,运用增重法评价了材料的腐蚀动力学规律,采用扫描电镜、能谱仪和Ｘ射线衍射仪分析了氧化膜形貌、结构和化学成分。结果表明,两种材料的腐蚀增重均服从抛物线生长规律,其中600合金的耐腐蚀性能优于304不锈钢;腐蚀500 h后,600合金表面氧化物厚度约为5 μm,主要成分为NiCr₂O₄,结构致密,具有保护性,其氧化膜及基体中均未发现明显渗碳行为;腐蚀500 h后,304不锈钢表面氧化膜可达约45 μm,为双层结构,外层为Fe₃O₄,内层为NiFeCrO₄,结构疏松,发生显著渗碳现象。本研究揭示了上述材料在超临界二氧化碳中的腐蚀机理,为超临界二氧化碳核反应堆结构材料的选择提供了数据支持。      

Transport of evaporated material through support gas in conjunction with ion plating: II

Following the first part of this work in which material transport through an inert support gas was treated on the basis of a diffusion model, calculations obtained using the Monte Carlo method are presented and compared with experimental results. The simulation of the particle trajectories is outlined, and an organigram of the mathematical procedure leading to the determination of the film thickness distribution on the substrate as well as on the chamber walls is given. Satisfactory agreement between the calculated data and experimental results for silver deposition at various argon pressures could be obtained by introducing a virtual particle source with a diameter that depends on the particle number density. Furthermore, results concerning the influence of the evaporation rate are discussed. The capabilities and limitations of the theoretical treatment with respect to ion plating conditions are reviewed and extended to include the effects of electrical discharges.     

Study on α-alumina precursors prepared using different ammonium salt precipitants

Nano-sized α-Al₂O₃ platelets have been produced by the precipitation method employing the starting material of Al(NO₃)₃·9H₂O and ammonium salt precipitants, such as the NH₄OH, (NH₄)₂CO₃ and NH₄HCO₃. The effects of chemical composition of ammonium salt precipitants and aging time of precipitated product on the formation of precursor and final product of α-Al₂O₃ particles were studied. The precursors with different crystal structures were formed depending on the chemical composition of precipitant and the agglomeration of final α-Al₂O₃ particles was found to be greatly affected by the precipitant. The aging time of precipitated precursor also influenced the agglomeration of final α-alumina particles.     

Ring compression properties of SiCf/SiC composites prepared by chemical vapor infiltration

SiC fiber reinforced SiC matrix (SiC_f/SiC) composites prepared by chemical vapor infiltration are one of promising materials for nuclear fuel cladding tube due to pronounced low radioactivity and excellent corrosion resistance. As a structure component, mechanical properties of the composites tubes are extremely important. In this study, three kinds of SiC_f preform with 2D fiber wound structure, 2D plain weave structure and 2.5D shallow bend-joint structure were deposited with PyC interlayer of about 150–200?nm, and then densified with SiC matrix by chemical vapor infiltration at 1050?°C or 1100?°C. The influence of preform structure and deposition temperature of SiC matrix on microstructure and ring compression properties of SiC_f/SiC composites tubes were evaluated, and the results showed that these factors have a significant influence on ring compression strength. The compressive strength of SiC_f/SiC composites with 2D plain weave structure and 2.5D shallow bend-joint structure are 377.75?MPa and 482.96?MPa respectively, which are significantly higher than that of the composites with 2D fiber wound structure (92.84?MPa). SiC_f/SiC composites deposited at 1100?°C looks like a more porous structure with SiC whiskers appeared when compared with the composites deposited at 1050?°C. Correspondingly, the ring compression strength of the composites deposited at 1100?°C (566.44?MPa) is higher than that of the composites deposited at 1050?°C (482.96?MPa), with a better fracture behavior. Finally, the fracture mechanism of SiC_f/SiC composites with O-ring shape was discussed in detail.     

Study on hot workability and optimization of process parameters of a modified 310 austenitic stainless steel using processing maps

To investigate the optimized hot deformation parameters of a modified 310 austenitic stainless steel, the hot compression tests were performed using a Gleeble 3500 thermal simulator. The hot deformation behavior and hot workability characteristics were investigated in a temperature range of 800–1100 °C and a strain rate range of 0.1–10 s⁻¹. The hot processing maps of the tested steel were developed based on the dynamic material model (DMM), from which the safe deformation regions and instable deformation regions were determined. The corresponding microstructural and hardness evolutions during deformation were analyzed in detail. It was found that the deformation in the safe regions was beneficial to dynamic recovery (DRY) and dynamic recrystallization (DRX), while the deformation in unstable region would lead to flow instability, kink boundaries and grain growth. Near 950 °C, the energy dissipation rates were unusually lower, and the hardness of the deformed sample exhibited a significant increase, as a result of strain-induced precipitation. Coupled with the microstructure analysis and processing map technology, the workability map was schematically plotted and the optimal working conditions were determined. Such conditions were: temperatures in the range of 1075–1100 °C and strain rates in the range of 0.5–1.7 s⁻¹. These conditions are critical to attain an excellent homogeneous microstructure with fine grains after deformation for the modified 310 austenitic stainless steel.     

Characterization and Interpretation of the Multiple Crystallographic Features of ε′ Precipitates in an Ag-Containing Mg-Sn Alloy

Metallurgical and Materials Transactions A - A novel orientation relationship (OR) between the ε′ precipitates and Mg matrix has been characterized in a Mg-Sn-Ag-Zn-Mn alloy. This OR is...     

反应堆控制棒材料Ag-In-Cd合金的压缩蠕变行为

研究了铸态Ag-In Cd合金在300—400℃及12—24 MPa压应力范围内的压缩蠕变行为,根据实验结果计算了表观应力指数n和表观激活能Q_a,探讨了合金的压缩蠕变机制.结果表明,随温度和应力的升高,合金的稳态蠕变速率增加,稳态蠕变速率与应力之间呈指数关系.温度为300,350和400℃时,合金的n分别为2.90,4.09和5.77;压应力为12,18和24 MPa时,合金的Q_a值分别为68.1,103.7和131.6 kJ/mol.位错运动形成大量层错是Ag-In-Cd合金在温度为300—400℃,压应力为12—24 MPa下的压缩蠕变控制机制.     

Effect of Al-doped ZnO film thickness on periodic GaAs subwavelength grating structures for photovoltaic device applications

We investigated the effect of Al-doped zinc oxide (AZO) films with different thicknesses deposited onto periodic cone-shaped GaAs subwavelength grating (SWG) structures on their physical properties. As the AZO deposition time was increased, the surface morphology of AZO deposited GaAs SWGs was changed. These structures exhibited the surface reflection of <～6.8% at 300–1200 nm because of their effective graded index distribution between air and the GaAs substrate via the AZO deposited GaAs SWGs, producing a lowest average reflectance of ～2.1% at 40 min of deposition time. With increasing the deposition time, the crystallinity of the AZO films deposited on GaAs SWGs was enhanced, which leaded to the decrease of the effective resistivity up to ～1.55 × 10^?3 Ω-cm at 100 min. The wetting behavior of a water droplet on the surface of samples was also studied.     

AL-6XN合金在超临界水中的应力腐蚀研究

采用慢拉伸试验研究了AL-6XN合金在550~650℃、25 MPa超临界水中的应力腐蚀行为,使用扫描电镜观察了材料断口形貌与标距面裂纹分布。结果显示:550℃试验条件下材料表现为穿晶开裂,标距面裂纹很多且分布较均匀,试样边角处出现扇形河流花样;650℃试验条件下材料表现为沿晶开裂,断口呈现典型的冰糖状,标距面裂纹数量大幅减少且集中于断口附近,相应的延伸率和断面收缩率也大幅降低。质子辐照对AL-6XN宏观力学性能影响不大,但导致试样断口的扇形花样(起裂源)数量增加,解理台阶宽度增大。以上结果表明,AL-6XN在超临界工况下具有严重的应力腐蚀开裂敏感性,升高温度和质子辐照会明显提高材料的应力腐蚀敏感性。     

Effect of Ni interlayer on partial transient liquid phase bonding of Zr–Sn–Nb alloy and 304 stainless steel

Zr–Sn–Nb alloy and 304 stainless steel were joined by means of partial transient liquid phase bonding. The effects of Ni interlayer on the microstructure and properties of the joints were investigated. The reaction layers are formed in both joints and which are mainly composed of σ-FeCr layer, Zr(Cr, Fe)₂ + α-Zr layer and α-Zr + Zr₂(Ni, Fe) layer. The intermetallic compounds are compact relatively and cracks are formed in the reaction layer of the direct bonded joint. In the joint with Ni interlayer, many α-Zr phases dispersedly exist in the reaction layer and the thickness of the reaction layer is distinctly larger than that without Ni interlayer. As a result of lower residual stresses and wider crack-free reaction layer, the bonding strength of the joint increases by using Ni interlayer.