稀土对38CrMoAl钢软氮化层抗冲蚀磨损性能的影响

研究了稀土元素对38CrMoAl钢软氮化层抗冲蚀磨损性能的影响. 结果表明: 与软氮化相比, 稀土软氮化提高了38CrMoAl钢的抗冲蚀磨损性能, 同时提高了软氮化层的硬度以及钢的冲击韧度. 由于软氮化时稀土的渗入, 改善了渗层组织, 从而提高了38CrMoAl钢的抗冲蚀磨损性能和机械性能. 扫描电子显微镜对冲蚀磨损试样表面形貌的观察发现, 普通软氮化层的磨损特征为塑性变形形成的犁沟剥落, 并伴随着萌生横向裂纹, 有大块磨屑剥落; 而稀土软氮化层则为塑性变形形成的犁沟剥落.     

降雨对532nm和1064nm激光传输的衰减特性研究

降雨会对激光信号产生严重的衰减,从而给激光目标探测的应用带来一定影响.激光在降雨中的传输衰减已在红外波段做了大量的实验研究,而可见光波段激光在雨中的传输衰减特性还未见报道.基于夫琅禾费衍射和几何光学散射理论,建立雨滴对532 nm绿激光和1064 nm近红外激光光束的传输衰减模型,对比分析两波长激光在不同降雨量下的衰减...     

热带对流活动日变化的模拟研究

利用一个云分辨与海洋的耦合模式,模拟研究了热带对流活动的日变化.通过对模拟结果的分析,揭示了热带地区不同海温日变化条件下,对流活动的云物理特征.利用热带海洋与全球大气响应观测实验（TOGA COARE）的观测资料作为模式的初始与边界场,来驱动耦合模式.对热带海表温度按照其日变化幅度的大小进行了分类,分为强、弱海表温度日变化两种类型,并在此基础上进行了合成分析.结果表明：1）在弱的海表温度日变化下,云中的云冰含量大于云水含量,说明云中以层状云为主;而在强的海温日变化下,云中的云水含量大于云冰含量,说明云中以 关键词： 热带对流日变化 地面降水率 云冰含量 云水含量     

基于1–10GHz空地链路信号的雨强监测方法可行性研究

空地链路上的微波信号受降雨影响, 会产生功率衰减和去极化效应. 基于这些物理特性, 本文提出利用1–10 GHz空地链路信号的降雨干扰项获取雨强的方法, 并开展了相关理论研究. 根据空地链路信号与雨滴复杂的相互作用, 研究了空地链路信号频率为1–10 GHz时, 雨强 (rain rate, R) 对衰减 (attenuation, A) 和交叉极化分辨率 (cross-polarization discrimination, XPD)的影响, 分别建立了A-R和XPD-R关系模型. 通过数值模拟, 分别分析了利用上述两个关系模型估测雨强的可行性, 并系统研究了不同频率、极化方式和仰角条件下的适用性. 研究结果表明, 对于水平极化或圆极化, 且频率较高的空地链路信号, 利用A-R关系反演强降雨具有理论上的可行性; 对于不同频率和极化方式的信号, XPD-R关系模型都可以用于反演雨强, 并且对于1–50 mm·h^-1范围内的雨强, XPD较为敏感; 不同仰角条件下, A-R和XPD-R 模型都适用. 在4–10 GHz时, 本文的XPD-R模型和国际电信联盟ITU-R中XPD预测模型的结果非常接近. 所得出的结论对于下一步开展相关的验证实验, 拓展卫星系统的气象应用, 实时估测降雨强度, 实现全球降雨观测具有重要的参考价值. 关键词： 空地链路信号 雨强 衰减特性 交叉极化分辨率(XPD)     

Damage characteristics and surface description of near-wall materials subjected to ultrasonic cavitation

For the analysis of ultrasonic cavitation erosion on the surface of materials, the ultrasonic cavitation erosion experiments for AlCu4Mg1 and Ti6Al4V were carried out, and the changes of surface topography, surface roughness, and Vickers hardness were explored. Cavitation pits gradually expand and deepen with the increase of experiment time, and Ti6Al4V is more difficult to erode by cavitation than AlCu4Mg1. After experiments, the cavitation damage characteristics such as the single pit, the rainbow ring area, the fisheye pit, and some small pits were observed, which can be considered to be induced by a single micro-jet impact, ablation effect caused by the high temperature, micro-jet impingement with a sharp angle, and multibeam micro-jets coupling impact or negative pressure in the local area produced by micro-jet impact, respectively. The surface roughness and Vickers hardness of the material increase slowly after rapid growth at different points in time as the experiment time increases. With the increase of the ultrasonic amplitude, both of them first increase and then decrease after the ultrasonic amplitude is greater than 10.8 μm. The increases in surface roughness and Vickers hardness tend to decrease as the viscosity coefficient increases. Ultrasonic cavitation can cause submicron surface roughness and increase surface hardness by 20.36%, so it can be used as a surface treatment method.     

Effect of pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel

The present work discusses the effect of the pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel. Cavitation erosion of three different types of the pearlitic steels (furnace-cooled, air-cooled, and forced-air-cooled) consisting of coarse, fine, and very fine microstructures were tested in 3.5% NaCl solution and compared with that of the as-received pearlitic rail steel. The variation in the mean depth of erosion (MDE) and mean depth erosion rate (MDER) with erosion time was analyzed. Furthermore, the cavitation erosion resistance of the as-received, the air-cooled, and the forced-air-cooled was found to be 1.03, 1.51, and 2.14 times better than the furnace-cooled pearlitic steel, respectively. It was concluded that the cavitation erosion resistance of the pearlitic steel increased with the increase in the fineness of the microstructure.     

Effects of Ce,Sm and Yb on cavitation erosion of NAB alloy in 3.5% NaCl solution

The influences of Ce, Sm and Yb on cavitation erosion of NAB alloy in 3.5% NaCl solution are evaluated using mass loss, SEM, 3D morphology and Tafel plot, respectively. The results show that the addition of Ce or Sm or Yb enhances the mechanical property of NAB alloy, and the sizes of κ_Ⅰ and κ_Ⅱ phases within NAB alloy decrease with adding Ce or Sm or Yb, resulting in the prevention of the propagation of the cracks caused by cavitation erosion initially originated at the phase boundaries between α and κ phases, and finally the cavitation erosion damage significantly decreases with adding Ce or Sm or Yb. The corrosion of NAB alloy in 3.5% NaCl solution can promote the cavitation erosion of NAB alloy, while the corrosion resistance of NAB alloy increases with the addition of Ce or Sm or Yb, and then the cavitation erosion resistance is accordingly improved with the addition of rare earth element.     

大脉冲电流下钨铜电极水和空气中的烧蚀特性

针对水中、空气中脉冲放电条件下金属电极烧蚀速率及烧蚀机理差异,对脉冲大电流作用下水中、空气中钨铜电极的烧蚀特性进行了对比研究。在保证放电电流波形一致性的前提下,通过采用高精度天平测量并获取了水中、空气中钨铜电极的阴、阳极烧蚀速率及总烧蚀速率,并对电极表面进行了二次电子观察和背散射电子观察分析。结果表明,大脉冲电流作用下,水中钨铜电极烧蚀较空气中更为严重,钨铜电极的烧蚀主要是金属蒸发引起的汽相侵蚀。由于水介质较空气具有不可压缩性,水中放电电弧集中,电极表面电弧斑点处电流密度和电流作用时间较空气中更为严重,同时由于水中脉冲放电时发生的高温物理化学反应,是造成水中电极烧蚀要高于空气中的根本原因。     

高气压大电流放电条件下的电极烧蚀

归纳了影响开关电极烧蚀量的因素,包括开关电极材料、放电条件等,分析了开关电极烧蚀特征与烧蚀后表面形貌,总结了开关电极烧蚀的主要机制电极加热和电极材料去除机制。为了延长开关工作寿命,提出了减少开关电极烧蚀的措施,包括选用抗烧蚀性能优异的材料作为开关电极材料、采用合适的开关电极结构和优化的放电条件等。