金属粉末气雾化技术研究新进展

气雾化制粉技术因粉末球形度高、气体杂质含量低等优点已经成为现在一种重要的粉末制备方法。雾化过程可粗略分为破碎和凝固两部分,涉及传热,物质交换以及多相流相互耦合等复杂现象。目前,人们对与雾化机理以及工艺参数的控制方法没有系统认识,制约了气雾化技术快速发展和工业化生产。本文简述了气雾化制粉中合金熔体的破碎行为机理,总结了最近几年关于气体流场结构、雾化工艺参数优化和计算流体力学在气雾化技术中的研究新进展,并且介绍了一些新技术在气雾化研究中的应用。     

金属雾化过程中气体流场动力学行为

利用流体动力学软件计算了喷射成形雾化室内气体的流场状态，分析了不同导液管出口长度对气体流动的影响，结果表明：雾化室内气体流速随轴向和轻向的位置变化而发生变化，距导液管出口处距离越远，气体速度越低，对于本文选用雾化器，当导液管出头长度小于1mm时，导液管内气体逆流，会造成金属反喷，导液管出口长度大于1mm时，导液管内气体向下流，产生对液态金属的抽吸作用，有利于喷射。     

Mechanism of Gas Intrusion into Molten Metal during Horizontal Centrifugal Casting

A mechanism of gas intrusion into molten metal during horizontal centrifugal castingwas introduced. Based upon this concept, a special pouring method was suggested, which caneffectively prevent the pinhole defects in horizontal centrifugal castings.     

气雾化球形金属粉末形成机理的研究进展

气雾化法是最早用来生产球形金属粉末的技术之一,有力地支持着3D打印技术的发展。由于粉末形成过程复杂,难以直接观察研究,为此研究人员采用仿真模拟的方法再现气雾化过程,揭示粉末形成机理。综述了气雾化过程中气流速度分布特征、金属熔体到粉末过程中破碎、球化、飞行、凝固的理论模型的研究成果,总结了影响粉末颗粒的形成过程相关的物理性能参数与工艺参数。最后指出气雾化制粉理论研究的发展趋势。     

Estimation of Cooling Rates During Close-Coupled Gas Atomization Using Secondary Dendrite Arm Spacing Measurement

Al-4 wt pct Cu alloy has been gas atomized using a commercial close-coupled gas-atomization system. The resulting metal powders have been sieved into six size fractions, and the SDAS has been determined using electron microscopy. Cooling rates for the powders have been estimated using a range of published conversion factors for Al-Cu alloy, with reasonable agreement being found between sources. We find that cooling rates are very low relative to those often quoted for gas-atomized powders, of the order of 10⁴ K s^?1 for sub-38 µm powders. We believe that a number of numerical studies of gas atomization have overestimated the cooling rate during solidification, probably as a consequence of overestimating the differential velocity between the gas and the particles. From the cooling rates measured in the current study, we estimate that such velocities are unlikely to exceed 20 m s^?1.     

Log-Normal Melt Pulsation in Close-Coupled Gas Atomization

High speed photography coupled with sophisticated image analysis has been used to study low-frequency pulsation during close-coupled gas atomization. At high gas pressure the instantaneous melt delivery is described by two superimposed log-normal distributions, one with a high standard deviation but little melt at the atomizer tip, the second with low standard deviation but more melt at the atomizer tip. At low gas pressures the distribution is better described by a single log-normal distribution.     

气雾化Al-Pb系轴瓦合金

采用气雾化技术，制备了应用于工业化ＲＳＰＭ工艺的高质量ＡｌＰｂ系合金粉末。对雾化粉末显微结构的分析表明，第二相（铅相）在基体中分布均匀，其粒径大小取决于凝固过程的冷速；不同粒径的粉末第二相分布随冷速的增加而分布更均匀、细化。对雾化粉末中各元素分布的分析表明，硅、铜等元素在晶界上有富积现象。     

真空熔炼高压气体雾化制粉技术及设备

介绍了气体雾化粉的品种、用途及工业化生产。还介绍了真空熔炼-高压气体雾化制粉所需的设备。     

多流气雾化工艺参数的研究

采用正交实验方法系统地研究了上层气流压力、下层气流压力、金属熔液温度、导液管突出高度对多流气雾化法工艺所制备粉末的平均粒径及粒度分布的影响，通过直观分析和方差分析，评价了各参数对粉末粒度的显著程度，优化了多流气雾化粉末制备法的丁艺参数。以焊锡63A为原材料的实验结果表明：最佳的工艺参数为上层喷嘴压力0．7MPa，下层喷嘴压力0．4MPa．金属熔液温度350℃．导液管突出高度为4mm；所制备粉末的平均粒径为6．3μm，粒度小于10μm的比例达到77．3％．且粒径分加曲线中的第一波峰值达到500nm左右，比现有报道的粒径分布曲线第一波峰值减小了一个数量级；     

金属熔体中夹杂物的生长动力学

在单颗粒框架下,对冶金熔体中夹杂物生长的两种主要形式“扩散反应析出”和“碰撞长大”进行适当的物理简化和数学建模,推导了夹杂物的生长速率,建立了夹杂物生长的动力学理论。利用该理论,解释了早期日本学者的实验结果,并对几种生长机理进行了定量比较。结果表明：从生长过程看,夹杂物的初期生长依赖于反应长大（起主要作用）和布朗运动碰撞,后期生长依赖于湍流碰撞（占主导地位）和Stokes碰撞;从流程看,碰撞长大在粗炼环节十分显著,在连铸环节基本可以忽略,而在精炼环节则处于过渡状况。     

气体压力对雾化颗粒大小的影响

文章研究了气体压力大小在雾化粉末工艺过程中的影响。结果表明,在限制式的喷嘴结构中,当熔体温度、气流喷射角度确定的条件下,气体压力较小,雾化颗粒不能形成,熔体会在导管中凝固或形成倒锥形的粘结块;随着气体压力的增加,粉末球化程度增大,平均颗粒减小。     

Momentum and Heat Transfer in Gas Atomization of Melts

Gas atomization of melt is widely used to produce metal powders and spray formed parts. In this process heat and momentum transfer of metal droplets take place during their flight in the gas medium. It is quite important to know the values of various parameters related to these two modes of transport phenomena. In the present paper mathematical models were developed and experimentally verified to predict values of various parameters, such as droplet and gas velocity, droplet temperature with time and distance travelled, percentage release of latent heat by the droplet. Four metals, lead, zinc, aluminium and tin were atomized to collect experimental data.     

金属锂在LiCl-KCl熔盐体系中的溶解过程

利用等温饱和法研究了温度对金属锂在LiCl-KCl熔盐体系中溶解度的影响。采用W电极,利用电流反向计时电位法和方波电流法研究了电流密度、LiCl含量对金属锂在熔盐中溶解速率的影响,并研究了极化对金属锂溶解速率的影响。结果表明,金属锂在LiCl-KCl中的溶解度随温度的升高而增大,在熔盐中的溶解反应为吸热反应,金属锂的溶解速率不受电流密度的影响,随LiCl含量的增加先增大后减小,溶解速率受熔盐体系黏度的影响较大。极化对金属锂溶解没有影响,锂的溶解没有电化学特性。     

Breakup of Gas Bubbles Rising in Molten Metals

A theory on the breakup of rising bubbles is developed on the basis of long‐term experiments with bubbles rising in different liquids. The probability of bubble breakup is expressed in terms of half‐life as a dimensionless function of the bubble volume and liquid properties. The results are applied to develop a mathematical model of bubbles rising in a column of high density liquid under a low external pressure. The model predicts that in typical steelmaking equipment the size of bubbles approaching the liquid level depends mostly on the external pressure and it is quite independent of the original size of the bubbles.     

Combined Low-Frequency and Electro-Impulse Treatment of Molten Metal

Metallurgist - A method is given for preparing alloy using combined low-frequency and electro-impulse action on a melt. Metallographic comparison is provided for the result of using this procedure...     

冷却水口降低钢水过热度的工业试验

 降低钢水的浇注过热度是提高连铸坯等轴晶率的有效措施。利用浸入水口冷却装置的导热平衡,设计气雾冷却水口装置和在线冷却介质检测与控制系统,在淮钢150 mm×150 mm方坯连铸机上进行冷却水口降低钢水过热度的初步工业试验,结果表明气雾冷却装置可以实现稳定操作,冷却介质在线调控系统可以满足浇注参数波动的需要,冷却芯导热系数与冷却芯/铜壁的界面热阻是影响传热的关键,降低浇注过热度约4 ℃。     

Capacitance and Impedance of Rhenium in Molten Alkali Metal Chlorides

The electrode capacitance is determined as a function of potential by measuring the capacitance and the impedance of a rhenium electrode in NaCl, KCl, and CsCl melts at various temperatures and ac signal frequencies, and the impedance parameters are calculated. The capacitance curve is shown to have two minima in these systems and an additional third minimum in sodium and potassium chlorides. This third minimum disappears when temperature increases. The potential of the cathode minimum of capacitance measured at an ac signal frequency of about 10³ Hz coincides with the corresponding minimum of the capacitance of the double electrical layer. The potentials of the central and anode minima of capacitance measured at a frequency of about 1 Hz coincide with the potentials of the minima of adsorption capacitance.     

气雾化工艺参数对金属粉末粒度影响的研究

气雾化生产金属粉末是一个复杂的过程，它涉及气体动力学、流体力学、冶金热力学等许多方面的知识，因而影响因素较多。从雾化工艺参数方面出发，研究了其对粉末粒度的影响，为工业生产提供了有益的参考。     

金属中气体分析进展

根据９０年代前期的一些文献,对测定金属中气体元素氢,氧、氮及碳,硫元素分析的有关方法做了综述。重点是关于有色金属、重金属、稀有金属中气体元素分析法。同时,介绍了一些有关冶金气体分析的现代仪器,并对助熔剂的选择等问题作了一些叙述．