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131.
The vapour phase compositions of a series of pack powder mixtures containing elemental Al and Hf or W powders as depositing sources and CrCl3·6H2O or AlF3or CrF3as activators were analysed in an attempt to further develop the pack cementation process to codeposit Al and Hf or W to form diffusion coatings on nickel base superalloys. The results suggested that Al could be codeposited with Hf, but not with W, from the vapour phase. Compared with both AlF3and CrF3, CrCl3·6H2O has been shown to be a more suitable activator for codepositing Al with Hf. The optimum coating temperature was identified to be in the range of 1050°C to 1150°C. Based on the thermochemical analysis, a series of coating deposition studies were undertaken, which confirmed that codeposition of Al and Hf could be achieved at a deposition temperature of 1100°C in the CrCl3·6H2O activated packs containing elemental Al and Hf powders. The coating obtained had a multilayer structure consisting of a Ni7Hf6Al16top layer and a NiAl layer underneath, followed by a diffusion zone, which revealed that the coating was formed by the outward Ni diffusion. It is suggested that the compositions suitable for codeposition of Al and Hf could be effectively identified by comparing the vapour pressures of HfCl4and HfCl3with that of AlCl in the packs activated by chloride salts. It has also been experimentally demonstrated that, although W could not be deposited from the vapour phase, a high volume of fine W particles can be entrapped into the outer NiAl coating layer formed by the outward Ni diffusion using a modified pack configuration. This leads to the formation of a composite coating layer with W particles evenly distributed in a matrix of NiAl. It is suggested that this modified pack process could be similarly applied to develop nickel aluminide coatings containing other refractory metals that may not be codeposited with Al from the vapour phase. 相似文献
132.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献
133.
Yong Zhang Yuanlong Mo Xiaolan Zhou Jianqing Li 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(12):2085-2094
Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). It has been shown in many experiments that the interaction efficiency and output power can be increased greatly by injecting plasma into the vacuum microwave device. Using field analysis, the dispersion characteristics and the interaction impedance of the disk-loaded waveguide filled with plasma are analyzed in a strong longitudinal magnetic field. In conclusion, the frequency of the TM01 mode increases as the density of the plasma increases. It also can be found when the plasma density increases to a large scale, the TM01 mode of the disk-loaded waveguide overlaps the TG mode, these two modes couple each other and form the new hybrid modes. 相似文献
134.
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136.
钻井井喷失控井喷流出口速度预测方法研究 总被引:6,自引:0,他引:6
失控井喷流出口速度、喷口内压力、喷层产量都是井喷失控处理方案设计、作业施工中重要的基础数据。由于井喷失控井井口环境条件复杂,井喷失控后无法在井口安装测量仪表及在高速喷流中放入参照物,不能直接获取以上数据。文章利用地质、钻井过程获得的地层物性参数和气体动力学方程,探讨井喷失控井天然气喷流在不同井筒流动尺寸及组合的喷流速度预测模型,可应用薄剪切模型或RNG修正的k-ε模型定量描述速度场、温度场、浓度场颁。为井喷失控井处理方案设计、施工作业提供基础数据。 相似文献
137.
中、高压变频器产量越来越多,但试验手段大多比较落后,一般采用带电机空转的方法。本文介绍了一个高压变频器试验平台,通过该平台可以对电压等级在3kV~10kV、功率在5000kW以下的变频器进行实载试验。 相似文献
138.
Lei Zhou Yu-Dong Yao Heffes H. Ruifeng Zhang 《Wireless Communications, IEEE Transactions on》2006,5(4):779-788
A reduced-rate retransmission (RRR) scheme is proposed for improving the throughput performance of spread-spectrum packet radio networks. The scheme takes advantages of the available multi-rate scalable source coding techniques. It assumes that several versions of a data packet with different sizes (number of information bits) are available. The transmission of a packet starts from its full-size version. If the full-size version is not correctly received, its half-size version is used in the retransmission. If further retransmissions are needed, the quarter-size version and so on are used. The shrunk packets are transmitted either in a minislot if the processing gain is kept the same, or occupying a slot duration by increasing the processing gain proportionally. In both cases, the effective signal to interference ratio for a packet is increased. As a result, the system throughput is improved. Theoretical and numerical results are provided in this paper which illustrate the throughput improvement. Another advantage of the proposed RRR scheme is that the packet-size reduction provides finer granules for link adaptation. Therefore, it is especially suitable for multimedia applications for which codes of variable rate for the source data are available and which can tolerate gracefully degraded quality of service. The performance of the proposed scheme in fading channels is also addressed. 相似文献
139.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
140.