Theoretical and Experimental Particle Velocity in Cold Spray

In an effort to corroborate theoretical and experimental techniques used for cold spray particle velocity analysis, two theoretical and one experimental methods were used to analyze the operation of a nozzle accelerating aluminum particles in nitrogen gas. Two-dimensional (2D) axi-symmetric computations of the flow through the nozzle were performed using the Reynolds averaged Navier-Stokes code in a computational fluid dynamics platform. 1D, isentropic, gas-dynamic equations were solved for the same nozzle geometry and initial conditions. Finally, the velocities of particles exiting a nozzle of the same geometry and operated at the same initial conditions were measured by a dual-slit velocimeter. Exit plume particle velocities as determined by the three methods compared reasonably well, and differences could be attributed to frictional and particle distribution effects.     

低铬不锈钢熔炼渣的实验研究

用CaCO3造渣,配加多种还原剂,进行了降低渣中Cr2O3铬损失的实验,还原效果均不明显且未达到泡沫渣的目的.CaC2加Fe-Si对渣中Cr2O3的还原效果最佳.实验结果表明,渣中FeO下降到2%以下,终渣中Cr2O3才能降低到5%以下,此时的CaO/SiO2需控制在1.5～1.8之间.实验过程中造渣剂与还原剂需分批多次加入,以防炉温降低太快,影响还原效果.     

Experimental Analysis of Spray Dryer Used in Hydroxyapatite Thermal Spray Powder

The spray drying process of hydroxyapatite (HA) powder used as a plasma spray powder on human hip implants was examined. The Niro-Minor mixed spray dryer was studied because it incorporates both co-current and counter-current air mixing systems. The process parameters of the spray drying were investigated: temperature, flow rate of the inlet hot air in the spray dryer, viscosity of feed/HA slurry, and responses (chamber and cyclone powder size, deposition of powder on the wall of spray dryer, and overall thermal efficiency). The statistical analysis (ANOVA test) showed that for the chamber particle size, viscosity was the most significant parameter, while for the cyclone particle size, the main effects were temperature, viscosity, and flow rate, but also their interaction effects were significant. The spray dried HA powder showed the two main shapes were a doughnut and solid sphere shape as a result of the different input.     

The Impact of a Partially Molten YSZ Particle

In plasma and high velocity oxy-fuel spraying, a certain portion of the injected powder is often not fully molten upon impact onto a substrate. We present numerical results of the impact of a partially molten yttria-stabilized zirconia particle, a material widely used as a thermal barrier. We consider an idealized scenario: the axisymmetric impact of a particle with a solid core, examining only the flow of the molten material around the core. The numerical method is based on the immersed boundary method for treating the interaction of solids and fluid within a computational domain. We present the results of a set of simulations, varying the particle and solid core diameters, and the impact velocity. When the core diameter is small relative to the particle, the impact behavior is similar to the impact of a fully molten droplet. When the core is larger, it promotes considerable splashing, which is undesirable.     

铝合金熔体中夹杂物与含氢量的关系

采用英国ＨＹＳＣＡＮⅡ测氢仪研究铝合金熔体中夹杂物与含氢量的关系,结果表明：在夹杂沾污度超过２．５％时,熔体含氢量会增另３倍以上;同时也研究了夹杂物尺寸和熔炼温度对含氢量的影响。     

Diagnostics of Cold-Sprayed Particle Velocities Approaching Critical Deposition Conditions

In cold spraying, the impact particle velocity plays a key role for successful deposition. It is well known that only those particles can achieve successful bonding which have an impact velocity exceeding a particular threshold. This critical velocity depends on the thermomechanical properties of the impacting particles at impacting temperature. The latter depends on the gas temperature in the torch but also on stand-off distance and gas pressure. In the past, some semiempirical approaches have been proposed to estimate particle impact and critical velocities. Besides that, there are a limited number of available studies on particle velocity measurements in cold spraying. In the present work, particle velocity measurements were performed using a cold spray meter, where a laser beam is used to illuminate the particles ensuring sufficiently detectable radiant signal intensities. Measurements were carried out for INCONEL^® alloy 718-type powders with different particle sizes. These experimental investigations comprised mainly subcritical spray parameters for this material to have a closer look at the conditions of initial deposition. The critical velocities were identified by evaluating the deposition efficiencies and correlating them to the measured particle velocity distributions. In addition, the experimental results were compared with some values estimated by model calculations.     

Inflight Particle Behavior in the Vacuum Kinetic Spray Process

The vacuum kinetic spray (VKS) process, also-called aerosol deposition, is a promising spray technology by which a thin or thick film can be fabricated at room temperature. Although a number of relevant studies have been performed, almost all have focused on the development of various applications, and unfortunately, the deposition mechanism has not yet been clarified. In this respect, the particle velocity in the flow field in VKS is investigated as a first stage of research into the VKS deposition mechanism. In this research, after a simulation prototype was derived based on the experimental results, the particle average and impact velocities were estimated. In addition, the change in particle velocities with gas flow rates, particle size, and working distance was analyzed based on simulation analyses and microstructural evidence. As a result, the gas flow rate, particle size, and working distance affect the particle impact velocity and further deposition behavior and film microstructure.     

Fabrication of Porous Molybdenum by Controlling Spray Particle State

In this study, porous molybdenum (Mo) was prepared by flame spraying of semi-molten particles with low velocity. The influence of spray particle parameters, including velocity and melting degree, on the microstructure and porosity of Mo deposit was investigated to understand the formation mechanism of the pore structure and connection between particles. The results showed that Mo spray particles with low velocity (<20 m/s) and semi-molten state can be generated by flame spraying. The Mo deposits with porosity from 39 to 61% were produced. High porosity in the deposit was achieved through the shielding effect of deposited particles. The surface-molten particles were bonded by the melt which flowed from surface to the particle/particle contact area. Moreover, the porosity decreased with the increase of melting degree of particles before impact. A 2D stacking model of semi-molten particles was proposed to explain the formation of bimodal pores and high porosity.     

The Effect of Torch Hardware on Particle Temperature and Particle Velocity Distributions in the Powder Flame Spray Process

Powder flame spray is a flexible, straightforward process. Particulate feed stock is heated and accelerated using an oxy-fuel flame. Liquid feed stock droplets impact the substrate, deform, and solidify to form a coating. Like other spray processes, coating microstructure and properties are directly related to particle velocity and temperature at the time of impact. Many controllable process inputs affect particle temperature and particle velocity. Data, from a series of designed experiments, exploring these factors and quantifying their significance are reviewed. These data show that multiple process inputs, especially torch hardware, can significantly affect particle temperature and velocity distributions in the powder flame spray process.     

Radiation Spectral Analysis and Particle Temperature/Velocity Measurement in Plasma Spray with One-Color Camera

A color camera optical diagnostic imaging system has been developed for the measurement of temperature and velocity of individual in-flight particles in thermal plasma spray, based on the principle of particle streak velocimetry and two-color thermometry. Radiation spectral analysis of the characteristic behavior of a particle-laden plasma plume was performed to identify an optimal spectral range for accurate temperature measurements over which the powder particles and the interfering thermal plasma gas are discernable. Calibration of the thermal imaging system was carried out using a blackbody furnace with uncertainties less than 1.8%. Extensive experimental measurements were taken with the optical imaging system to obtain the temperature and velocity distributions of YSZ particles in practical plasma spraying applications. The uncertainties of the measured temperature and velocity with a color camera system mostly fluctuate around ±10% in comparison with data obtained from a commercially available measuring system.     

铝液精炼的探析

精炼是熔炼工艺中重要的环节,其目的就是去除铝液中的气体、非金属化合物和其他有害元素,使铝液得到净化,从而提高铝液质量.精炼包含铝液的净化和除气两部分.     

Improving Atmospheric Plasma Spraying of Zirconate Thermal Barrier Coatings Based on Particle Diagnostics

Lanthanum zirconate (La₂Zr₂O₇) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of La₂Zr₂O₇ a considerable amount of La₂O₃ can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La₂O₃-ZrO₂ system, in the composition range of pyrochlore structure, the stoichiometric La₂Zr₂O₇ has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro?-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on gadolinium zirconate (Gd₂Zr₂O₇) were included, which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings that show good thermal cycling performance.     

Numerical Study of In-flight Particle Parameters in Low-Pressure Cold Spray Process

A 2-D model of the low-pressure cold spray with a radial powder feeding was established using CFD software in this study. The flow field was simulated for both propellant gases of nitrogen and helium. To predict the in-flight particle velocity and temperature, discrete phase model was introduced to simulate the interaction of particle and the supersonic gas jet. The experimental velocity of copper powder with different sizes was used to validate the calculated one for low-pressure cold spray process. The results show that the computational model can provide a satisfactory prediction of the supersonic gas flow, which is consistent with the experimental Schlieren photos. It was found that similar velocity was obtained with the drag coefficient formula of Henderson and with that of Morsi and Alexander. As the shape factor was estimated, the reasonable prediction of velocity for non-spherical particle can be obtained, to compare with the experimental results.     

Improving Powder Injection in Plasma Spraying by Optical Diagnostics of the Plasma and Particle Characterization

Powder injection parameters such as gas flow, injection angle, and injector position strongly influence the particle beam and thus coating properties. The interaction of the injection conditions on particle properties based on DPV-2000 measurements using the single-cathode F4 torch is presented. Furthermore, the investigation of the plasma plume by emission computer tomography is described when operating the three-cathode TriplexPro? torch. By this imaging technology, the three-dimensional shape of the radiating plasma jet is reproduced based on images achieved from three CCD cameras rotating around the plume axis. It is shown how the formation of the plasma jet changes with plasma parameters and how this knowledge can be used to optimize particle injection.     

Cu粉含量对PTFE基复合材料导热性能影响的数值分析

利用ANSYS参数化有限元分析技术,分析铜粉颗粒均匀分布于PTFE基复合材料的温度分布规律及其有效热导率与铜粉含量的关系,并与试验结果进行了对比。结果表明,铜粉含量对PTFE基复合材料的导热性能有显著影响,其含量与热导率接近线性关系。数值分析结果与试验结果相吻合,说明了模拟结果的可靠性。本研究结果将为PTFE基复合材料的高导热性能设计和应用提供参考。     

铝熔体测氢仪原理及进展

本文介绍了几种常用则氢仪的工作原理,并着重介绍了国产ＥＬＨ－ⅢＢ型测氢仪的特点和性能。通过对Ａ３５６合金在不同熔炼条件下氢含量的测定,验证了ＥＬＨ－ⅢＢ型测氢仪具有较高的使用价值。     

Study of the Influence of Particle Velocity on Adhesive Strength of Cold Spray Deposits

The adhesion mechanism of deposit/substrate interface prepared by the cold spray method is not fully understood at present. It seems that the adhesion strength is mainly determined by the mechanical (including the plastic deformation of particle and substrate) and thermal interaction between particle and substrate when the particles impact onto the substrate with a high velocity. In order to understand the adhesion mechanism, a novel adhesive strength test was developed to measure the higher bonding strength of cold sprayed coatings in this study. The method breaks through the limits imposed by glue strength in the conventional adhesive strength test, and it can be used to measure the coatings with a higher adhesive strength. The particle velocity was obtained with DPV-2000?measurement and CFD simulation. The relationships between the adhesion strength of deposits/substrate interface and particle velocity were discussed. The results show that stronger adhesion strength can be obtained with the increase of particle velocity. There are two available ways to improve the adhesion strength. One is to increase the temperature of working gas, and another is to employ helium gas as the working gas instead of nitrogen gas.     

基于灰关联分析的多元线性回归模型对铁液含硅量的预测

铁液含硅量是表征高炉炉温等不可准确检测状态的反应量,准确预测可帮助高炉冶炼人员及时了解炉内信息。本文运用灰关联分析方法,提取20个影响含硅量预测因素中的6个作为主要影响因素,然后建立多元线性回归滑动预测,预测命中率在90％左右,相对误差为0．0178。     

Effect of Ceramic Particle Velocity on Cold Spray Deposition of Metal-Ceramic Coatings

In this paper, metal-ceramic coatings are cold sprayed taking into account the spray parameters of both metal and ceramic particles. The effect of the ceramic particle velocity on the process of metal-ceramic coating formation and the coating properties is analyzed. Copper and aluminum powders are used as metal components. Two fractions of aluminum oxide and silicon carbide are sprayed in the tests. The ceramic particle velocity is varied by the particle injection into different zones of the gas flow: the subsonic and supersonic parts of the nozzle and the free jet after the nozzle exit. The experiments demonstrated the importance of the ceramic particle velocity for the stability of the process: Ceramic particles accelerated to a high enough velocity penetrate into the coating, while low-velocity ceramic particles rebound from its surface.     

Measurement of the Particle Velocity in a HVOF Spray with PIV Under Industrial Conditions

The particle velocity and the particle temperature are two of the most important parameters influencing the deposition process of high-velocity oxy-fuel (HVOF) spraying. This article addresses the application of particle image velocimetry to the measurement of the 2D particle velocity distribution in the flame of an industrial burner in a spraying booth under industrial conditions. Therefore, the measurement equipment has to be protected from overspray. Moreover, the low particle number density of HVOF sprays requires a technique called average correlation for image evaluation. The effect of the variation of process parameters, such as oxygen flow rate and mass loading of the flame, on the particle velocity is discussed.