Hot deformed anisotropic nanocrystalline NdFeB based magnets prepared from spark plasma sintered melt spun powders

Anisotropic magnets were prepared by spark plasma sintering (SPS) followed by hot deformation (HD) using melt-spun powders as the starting material. Good magnetic properties with the remanence J_r > 1.32 T and maximum of energy product (BH)_max > 303 kJ/m³ have been obtained. The microstructure evolution during HD and its influence on the magnetic properties were investigated. The fine grain zone and coarse grain zone formed in the SPS showed different deformation behaviors. The microstructure also had an important effect on the temperature coefficients of coercivity. A strong domain-wall pinning model was valid to interpret the coercivity mechanism of the HDed magnets. The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. The polarization characteristics of HDed magnets were demonstrated. It was found out that the HDed magnets had better corrosion resistance than the counterpart sintered magnet.     

深亚微米MOSFET衬底电流的模拟与分析

利用器件模拟手段对深亚微米ＭＯＳＦＥＴ的衬底电流进行了研究和分析，给出了有效的道长度，栅氧厚度，源漏结深，衬底掺杂浓度以及电源电压对深亚微米ＭＯＳＦＥＴ衬底电流的影响，发现电源电压对深亚微米ＭＯＳＦＥＴ的衬底电流有着强烈的影响，热载流子效应随电源电压的降低而迅速减小，当电源电压降低到一定程度时，热载流子效应不再成为影响深亚微米ＭＯＳ电路可靠性的主要问题。     

格子砖热工特性对蓄热室内换热的影响

分析了热风炉蓄热室内各时期的基本传热形式,建立了其传热过程的数学模型。针对首钢2号高炉1#热风炉进行了实例计算,通过对模型计算值与实测值的比较分析,表明本模型具有较好的适用性。对比分析了几种不同几何参数的格子砖的换热情况,结果说明,在新建和改造的热风炉上采用十九孔格子砖将可获得良好的热工指标。     

深部高瓦斯低透气性煤层水力挤出效果研究

阐述了水力挤出措施的工艺流程、钻孔布置和注水系统设备选型,考察了注水前后煤体应力的变化情况和钻孔有效影响范围,分析了水力挤出措施实施前后瓦斯涌出特征及规律。研究表明,在深部高瓦斯低透气性煤层采用水力挤出措施,可有效增强煤层透气性,减小瓦斯应力,降低瓦斯涌出量和涌出速度,防突效果明显。     

多向挤压对AZ80镁合金组织与性能的影响

研究多向挤压工艺对铸态AZ80镁合金组织和性能的影响。随着挤压道次的增加,材料晶粒得到明显细化,再结晶数量不断提升,组织为细小均匀的等轴晶,材料性能得到提高。经过4道次的挤压,材料组织性能达到最优,晶粒尺寸为6.6μm,屈服强度为214.3 MPa,抗拉强度为304.6 MPa,断后延伸率为10.75%,显徽硬度为83.6。     

铜扁线生产的连续挤压工艺

介绍铜扁线生产的传统的拉拔方法和连续挤压方法，论述连续挤压方法生产铜扁线所具有的优点。两种工艺方法所生产的铜扁线的组织比较分析表明，连续挤压法是一种优于传统工艺的铜扁线生产方法。     

Hot Deformation Behavior of an As—cast Duplex Stainless Steel

The hot deformation behavior of an as-cast 0Crl7Mnl4Mo2N duplex stainless steel has been studied by hot com-pression test at the temperature range from 1000℃ to 1200℃, and the strain rates are 0.1 s^-1, 1 s^-1 and 5 s^-1,respectively. It was found that during hot deformation there is only dynamic recovery taking place within the δ-ferrite phase, but the γ-austenite phase undergoes dynamic recrystallization. The activation energy of the steel for hot compression is estimated to be 480 kJ/mol.     

Sialon陶瓷热挤压模的应用研究

用Ｓｉａｌｏｎ陶瓷取代３Ｃｒ２Ｗ８Ｖ钢进行热挤压模的应用试验，取得良好效果，并对与应用相关的陶瓷材料抗热震性和磨损性能进行了研究。     

A comparison of the microstructure of silicon nitride-silicon carbide composites made with and without deoxidized starting material

Two different types of silicon carbide (SiC) matrix composites, with either 10 wt% or 20 wt% silicon nitride (Si₃N₄) reinforcement, were fabricated to investigate the effect of pretreatment on the resulting composite micro-structure. The first type of composite was prepared from as-received α-SiC and α-Si₃N₄ powders, while the second type was prepared from powder compacts that had been deoxidized to eliminate surface silica on the powder particles. The composites were hot isostatically pressed in tantalum cans at 2373 K for 1h under a pressure of 200 MPa. Density measurements showed that full theoretical density was achieved for the composites prepared from the as-received powders, while much lower densities were obtained for the composites prepared from the deoxidized green compacts. Almost all of the α-SiC transformed into β-SiC, and almost all the α-Si₃N₄ transformed into α-Si₃N₄ in the composites made from the as-received powders, while in the composites made from the deoxidized material the α-SiC remained untransformed and both α-Si₃N₄ and β-Si₃N₄ phases were present in significant quantities. High-resolution transmission electron microscopy and Fresnel fringe imaging were used to identify the grain boundary and interphase boundary structure. Most interfaces were found to be covered with ? 1 nm thick amorphous intergranular films in the composites prepared from as-received powders, whereas most interfaces were found to be free of such amorphous intergranular films in the composites prepared from the deoxidized material. Taken together, the presence of intergranular films at the interfaces and the results from density measurements are consistent with the densification and reverse α → β-SiC transformation taking place in the composites made from as-received powders by a liquid-phase sintering route. An incomplete liquid-phase sintering mechanism is also able to explain the microstructure observed in the composites made from the deoxidized material.     

Effects of solid lubricants in backward extrusion

In the present paper, some solid lubricants were tested in backward extrusion friction tests with flat-headed punches using aluminium at room temperature. The results showed that anti-seizure ability was improved when wax was added to the solid lubricant samples. In addition, a water-based graphite lubricant and an ultrahigh molecular weight polyethylene (UHMW-PE) lubricant were tested using aluminium workpieces heated to 500°C. The lubricity of the UHMW-PE lubricant was found to be superior to that of the graphite lubricant.