球磨转速对含钆ODS钢中M23C6析出的影响研究

以“结构/屏蔽一体化”为研发目标的含钆ODS合金具有较优的中子屏蔽性能与高温力学性能,可作为小型模块化铅冷快堆中子屏蔽材料的研发方向之一。在机械合金化-放电等离子体烧结工艺制备含钆ODS-316L钢的研究中发现,球磨转速影响材料的析出相种类,如在220 r/min低球磨转速下,ODS-316L钢中仅存在纳米尺寸的Gd-Si-O析出相,而在300 r/min高球磨转速下,除纳米尺寸的Gd-Si-O析出相外,材料内还分布着大量百纳米尺寸的片层堆叠状M₂₃C₆型碳化物,且M₂₃C₆内同样存在纳米含钆氧化物颗粒。高球磨转速使球磨粉内元素的偏析与内应力的累积促进了M₂₃C₆的形核,随后的粉末烧结温度则为M₂₃C₆的生长提供了驱动力。此研究可为粉末冶金含钆ODS-316L钢的微观组织调控奠定一定的实验与理论基础。     

Modeling of Nucleation and Growth of M23C6 Carbide in Multi-component Fe-based Alloy

Three-dimensional atom probe (3DAP) technique has been used to study the nucleation and growth of M23C6 carbide in a supersaturated multi-component Fe-based alloy aged at 800°C. 3D images indicate that the radius of M23C6 carbide after ageing for 10 min is about 9 nm. Concentration profiles of alloy elements in the carbide are also obtained. Combined with PANDAT and Thermo-Calc software, attempts to model the early stages of precipitation are present. The calculated particle size and composition of M23C6 carbide is in good agreement with 3DAP data.     

Precipitation and thermal instability of M23C6 carbide in cast Ni-base superalloy K452

During long-term thermal exposure M₂₃C₆ dendritically precipitates from the supersaturated γ matrix and then changes in shape from flower-like dendrite to irregular block to regular polyhedron. The reduction in the interfacial energy is responsible for the morphological transition, but the stable morphology of the carbide is principally determined by the anisotropy of the interfacial energy between the carbide and the γ' in the M₂₃C₆-γ' cell. In addition, M₂₃C₆ has a negligible influence on the tensile property of the thermally exposed alloy even though it can block the mobile dislocations and stacking faults to some extent.     

On the normal and superconducting properties of Ba6C60

From SQUID measurements we determine the basic critical magnetic field values for bcc phase Ba₆C₆₀ superconductor and hence evaluate the major parameters of superconductivity in this material. A comparative analyses of these parameters observed for the alkaline-earth-doped vs. alkali-metal-doped C60 superconductors is presented. These two systems are found to differ substantially in their superconducting properties: for Ba₆C₆₀ we find that the upper critical fieldH _c 22 T, and the Ginzburg-Landau parameter15, as compared to the values 50 T and 100, respectively, for superconducting K₃C₆₀. On the other hand, the electronic properties for all the superconducting fullerenes are rather similar with, for example, the Fermi energyE _F0.1 eV.     

Cr3C2对WCoB-TiC金属陶瓷组织和性能的影响

以WC、TiB2和Co粉末为原材料,采用原位反应液相烧结工艺,在1400℃真空烧结炉中制备了WCoB-TiC复相金属陶瓷.利用FE-SEM、EDS和XRD等技术,研究了不同含量晶粒长大抑制剂Cr3C2对WCoB-TiC金属陶瓷组织和性能的影响.结果表明,添加Cr3C2能有效抑制WCoB-TiC金属陶瓷晶粒异常长大,使得材料获得更均匀细小的微观组织,并且提高硬度和耐磨性能.随着抑制剂Cr3C2含量的增加,金属陶瓷的晶粒更细小均匀(晶粒尺寸可达1.0μm),硬度随之升高到91.0HRA,并且耐磨性能得到明显改善,磨损损失质量远小于未添加Cr3C2的试样.     

Production of single-crystal K3C60

A simplified technique for synthesizing high-quality millimeter-sized single-crystals of K₃C₆₀ is reported. The preparation method consists of a two-step process where pure C₆₀ crystals are first grown and later doped with potassium vapor. The undoped crystals are grown using an open-tube vapor transport with a flowing helium gas carrier. Doping occurs in a highvacuum environment inside a specialized quartz tube which allows phase purity to be monitored via magnetization measurements of the superconducting state. Utilizing the aforementioned procedure, one can attain samples with magnetically determined superconducting transition widths (10–90% diamagnetic shielding) of less than 1 K.     

Microstructure evolution and mechanical properties of 316H weld metal during aging

ABSTRACT

A standard 316H welding wire was used to obtain 6% δ-ferrite in the weld metal by the automatic tungsten inert gas welding. The effect of aging time at 750°C on microstructure and mechanical properties of the weld metal were analysed. The results showed that as the aging time increased, the δ-ferrite fraction decreased, and finally, δ-ferrite was no longer seen, the M₂₃C₆ fraction first increased and then decreased, and the σ phase fraction increased. Finally, the fractions of M₂₃C₆ and σ phase kept stable, but the size increased. Accordingly, as the aging time increased, the yield and tensile strengths first decreased significantly, then increased obviously and finally decreased slightly again, while the elongation and impact energy decreased all the time.     

Formation of lamellar M23C6 on and near twin boundaries in austenitic stainless steels

Thin foil electron microscopy studies were made on the precipitation of lamellar M₂₃C₆ during aging at 973 K and 1073 K in water-quenched specimens of two austenitic stainless steels. After the precipitation on incoherent twin boundaries M₂₃C₆ formed on coherent twin boundaries and in the regions adjacent to incoherent twin boundaries. These precipitates showed lamellar morphology and were aligned in a specific manner with respect to the twin boundaries. Such lamellar precipitates were absent in the specimens which were isothermally treated at 1073 K after being transferred from the solution treatment temperature. The lamellar morphology of M₂₃C₆ is suggested to be developed by the influence of residual specific stress field around twin boundaries resulted from quenching.     

Mild solvothermal synthesis of complex fluorides Li2BeF4 and LiSrAlF6

The complex fluorides Li₂BeF₄ and LiSrAlF₆ were synthesized solvothermally at 180–240 °C and characterized by means of X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The different influence factors such as solvents, molar ratios of initial mixtures, reaction temperature and reaction time were investigated. The experimental results indicated that Li₂BeF₄ and LiSrAlF₆ powders could be controllably synthesized in the solvothermal process.     

Dissolution of laves phase by re-austenitization and tempering of creep strength enhanced ferritic steel

ABSTRACT

Formation of Laves phase in creep strength enhanced ferritic steel is investigated using re-austenitization and tempering treatment. The as-received material is exposed to 620°C for 4560?h aging, and then re-austenitizated at 1050°C for 1?h, and followed by tempering at 760°C for different times (2 and 4?h). After re-austenitization and tempering, the dissolution of Laves phase is observed while grain size and microhardness have not changed significantly. A model is suggested to quantify the dissolution of W-containing Laves phase. Thermo-Calc is used to predict driving forces for precipitation of Laves and M23C6 phases.     

Synthesis of Ti3Si0.8Al0.4C1.8 solid solution from Ti-Si-Al-C powder mixture

In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti₃Si_0.8Al_0.4C_1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti₃Si_0.8Al_0.4C_1.8 solid solution. XRD results showed that predominantly single phase samples of Ti₃Si_0.8Al_0.4C_1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti₃Si_0.8Al_0.4C_1.8 lay between those of Ti₃SiC₂ and Ti₃AlC₂. SEM observation showed that the grains of Ti₃Si_0.8Al_0.4C_1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti₃SiC₂ and Ti₃AlC₂.