添加混合稀土的廉价Nd-Fe-B的研究

Nd-Fe-B永磁材料不仅具有很高的磁性能 ,而且不含资源紧缺的战略物资钴 ,因而其应用前景非常广阔。但人们希望其价格再降低 ,所以开发廉价磁体非常必要。可以通过降低原材料的成本 ,达到降低磁体成本的目的。实验对以混合稀土取代Nd Fe B合金中的钕的廉价铁基稀土永磁进行了研究 ,结果表明 :随着混合稀土的增加 ,磁性能有所下降 ,但在合金中添加少量的Al,Co,Nb ,可使磁体的磁感矫顽力 BHC上升 ,剩余磁感应强度Br、磁能积 (BH) m稍有下降。     

Towards a more comprehensive microstructural analysis of Zr-2.5Nb pressure tubing using image analysis and electron backscattered diffraction (EBSD)

Zr-2.5Nb pressure tubes used in CANDU (CANada Deuterium Uranium) reactors have a very complex microstructure, with two major crystallographic phases, α and β. These phases include a fair amount of deformation from the extrusion process and the cold working (∼25%) performed at the end of the manufacturing process. This microstructure (texture, grain aspect ratio, etc.) changes along the tube’s length and differs from tube to tube. In order to better understand the deformation mechanisms, these microstructural differences must be statistically characterized. Scanning electron microscopy combined with direct image analysis or with electron backscattered diffraction (EBSD) are good techniques for carrying out such a measurement. However it is not possible, using specimen preparation methods specific for each of these techniques, to reveal all of the grain and phase boundaries. We have thus developed post-treatment algorithms to be able to partially analyze the revealed Zr-2.5Nb microstructure. The first algorithm was used for image analysis treatments of micrographs taken at 5 kV on the radial-tangential plane of etched samples using a reactive ion etch (RIE, CF₄ + O₂). The second was developed for EBSD grain mapping and can be used to characterize α-Zr grain shape and orientation. The two techniques are complementary: EBSD gives information about the micro-texture and the relationship between the microstructure and micro-texture while image analyses of SEM micrographs reveal the direction and distribution of the α-Zr lamellae more easily and over a greater sample area than EBSD. However, the SEM micrographs that were used did not reveal any grain boundary (only phase boundary). An analysis of EBSD grain maps reveals that the average α-Zr grain size, mainly in the elongated direction (tangential), is smaller than what is normally obtained from an image analysis of SEM micrographs. The grain size distribution of type I α-Zr grains (deformed original (prior) α-Zr) and type II (stress-induced β-Zr → α-Zr phase transformation) is also shown to be different for sizes greater than 0.4 μm².     

Effect of microstructure on the corrosion of CVD-SiC exposed to supercritical water

Silicon carbide (SiC) is an important engineering material being studied for potential use in multiple nuclear energy systems including high-temperature gas-cooled reactors and water-cooled reactors. The corrosion behavior of SiC exposed to supercritical water (SCW) is critical for examining its applications in nuclear reactors. Although the hydrothermal corrosion of SiC has been the subject of many investigations, the study on the microstructural effects on the corrosion is limited. This paper presents the effect of residual strain, grain size, grain boundary types, and surface orientations on the corrosion of chemical vapor deposited (CVD) β-SiC exposed to SCW at 500 °C and 25 MPa. Weight loss occurred on all the samples due to localized corrosion. Residual strains associated with small grains showed the most significant effect on the corrosion compared to the other factors.     

First-principles investigation of energetics and site preference of He in a W grain boundary

We perform first-principles calculations based on density functional theory to investigate energetics and site preference of He in a bcc-W Σ = 5 grain boundary (GB). The segregation energy is calculated to be −1.37 eV, indicating that He prefers to segregate in the W GB. The formation energy of He in the W GB is positive and thus He is quite hard to dissolve in the W GB, similar to its behavior in the bulk. Because of its closed-shell electronic structure, He is shown to preferably occupy either interstitial or substitutional site with larger space provided by the GB, changing the GB electronic structure. Moreover, segregation of He gives rise to the W GB expansion. These structure variations can have a large effect on the mechanical properties of the W GB.     

Two-step two-stage fission gas release model

A two-step two-stage model is developed in this study on the basis of the recent theoretical model. This model incorporates a two-step burn-up factor in the two-stage diffusion processes in the grain lattice and at the grain boundary during the fission gas release. In-pile data sets available in FRAPCON-3 code are used to validate the model. Results show that the predictions are in better agreement with the experimental measurements than those of any other models built in the code over the entire burn-up range up to 75 000 MWd/MTU.     

基于web的核心交换机性能监测系统的实现

本文介绍了一种校园网核心交换机性能监测系统的设计与实现,它通过SNMP协议定时对交换机上的MIB数据库的性能参数进存采集,并将统计分析的结果以图形的形式显示给用户。     

Effect of substituting Mm with La on the electrochemical performances of Co-free LaxMm1−x(NiMnSiAlFe)4.9 (x = 0–1) electrode alloys prepared by casting and rapid quenching

In order to enhance the electrochemical capacity of the Co-free AB₅-type electrode alloy, Mm in the alloys was substituted with La and Co-free La_xMm_1−x(NiMnSiAlFe)_4.9 (x = 0, 0.45, 0.75, 1.0) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substituting Mm with La on the electrochemical performances of the as-cast and quenched alloys were investigated in detail. The obtained results show that substituting Mm with La can enhance markedly the capacities of the as-cast and quenched alloys. When the amount of substituting Mm with La, x increased from 0 to 1.0, the maximum capacity of the as-cast alloys at 0.2C rate increased from 273.45 to 304.47 mAh g⁻¹, and the capacity retaining rate (R_h) increased from 59.16 to 59.86%. The capacity of the as-quenched alloys with a quenching rate of 10 m s⁻¹ increased from 236.83 to 300.31 mAh g⁻¹, and the capacity retaining rate (R_h) decreased from 78.69 to 62.29%. The substituting Mm with La had an insignificant effect on the activation capabilities of the as-cast and quenched alloys.