超音速等离子喷涂参数对粒子速度温度的影响

采用高效能超音速等离子喷涂系统,选用纯Al2O3粉末,研究了电功率、电流、电压、气体流量、送粉量对飞行粒子速度和温度的影响.研究结果表明:Al2O3粒子的温度、速度随功率的增大分别呈持续上升与先增大后下降的趋势;在相同功率时,电流对粒子速度、温度的影响大于电压的影响;加大主气流量,粒子速度和温度均先增大后减小;增大送粉量,粒子速度先增大后减小,而粒子温度则一直减小.最后结合涂层的形貌、孔隙率、显微硬度,优化出最佳的喷涂参数.     

等离子喷涂送粉参量对粉末粒子运动行为的影响分析

为研究等离子喷涂设备送粉参量变化对粉末粒子运动行为的影响,通过数学计算给出了粉末粒子初速度及运行轨迹的一些解析计算结果.结果表明粉末粒子喷出初速度随送粉气流量的增大呈线性增大,随送粉管直径增大呈指数减小,而且与密度和粒径的指数幂成反比关系.当粉末粒子粒径为75μm时,Ni金属粉末的最佳送粉参量为:送粉气流量0.2m3/h,送粉管直径1.5mm;Al2O3陶瓷粉末最佳送粉参量为:送粉气流量0.3m3/h,送粉管直径1mm.该项研究工作为选择最佳送粉参量和控制粉末粒子在等离子流场中的运动提供了依据.     

等离子喷涂工艺参数对粒子速度和温度的影响

在G型喷嘴下，利用SprayWatch-2i喷涂粒子速度、温度测试仪在线测量粒子的飞行参数，研究了等离子喷涂工艺参数对喷涂粒子速度和温度的影响，并对等离子喷涂氧化锆粉末的主要工艺参数进行优化分析。在诸因素中．气体流量对粒子速度和温度的影响最为显著，随着主气流量的增加，粒子速度有所增加。     

等离子喷涂参数对TiB2可湿润阴极涂层沉积效率的影响

采用大气等离子喷涂（APS）在石墨质碳阴极材料上沉积TiB2可湿润性阴极涂层。研究了喷涂工艺参数对涂层沉积效率的影响。结果表明,涂层沉积效率随喷涂距离的增加而增加,随主气流量、喂料速率和喷涂功率增加呈现出先增加后减少的趋势,随粉末尺寸的减少而增加。最佳工艺参数为：喷涂距离80 mm,主气流量1900 L/h,送粉气流量（Ar）120 L/h,喂料速率27.34 g/min,喷涂功率35.8 kW,颗粒直径(d50) ≤37.4 μm,该条件下涂层沉积效率为67.26%。该TiB2涂层在220 kA铝电解槽上应用,槽稳定后铝液中Ti含量为0.0021%（质量分数）。     

等离子喷涂流场分布及颗粒运动特性（英文）

考虑了化学反应及压力梯度力,对等离子喷涂流场分布及颗粒运动特性进行研究。利用Spray Watch-2i对飞行颗粒进行在线监测。结果表明:气流的最高温度为12000 K,最高速度为150 m/s。当载气流量在4 L/min时,颗粒能够很好的加热加速。当送粉流道与射流方向垂直时,颗粒分布在流场外围,而当送粉流道与流场垂直方向倾斜8°夹角后,颗粒的运动轨迹偏向流场中心。当颗粒直径为10μm时,颗粒能够被载气送入到射流中心位置。而当颗粒直径逐渐增大时,颗粒穿过射流中心分布在流场外围。颗粒的最大速度达到270.9 m/s,最大温度达到3939 K。最佳喷涂距离为80 mm。     

喷嘴下游形状对冷喷涂粒子加速行为影响的数值模拟研究

目的 冷喷涂过程中喷嘴内流道关键尺寸是影响粒子加速的重要因素。虽然喷嘴下游长度与扩张比是喷嘴的2个最重要参量,但目前对喷嘴优化设计的研究仍有深入空间,比如喷嘴下游形状。方法 本文利用计算流体动力学的软件ANSYS/Fluent进行数值模拟研究,在与传统锥形下游相比较后,设计了钟形下游与喇叭形下游喷嘴。同时研究了喷嘴下游形状对气流与粒子加速行为的影响。结果 对于钟形下游喷嘴,其气流速度在过喉部后迅速增加到较高数值,随后变化缓慢;对于喇叭形下游喷嘴,其气流速度在过喉部后先增加缓慢,直至截面积开始快速增加时,气流速度迅速增加;喷嘴下游形状对粒子撞击基板时的速度有一定影响,且随着喷嘴下游长度和粉末粒度的变化而改变。对于Cu粉,当为下游100 mm短喷嘴时,锥形下游喷嘴对10~20 μm的粒子加速效果最好。当粉末在20 μm以上时,喇叭形下游喷嘴的加速效果最好。对于下游220 mm长喷嘴,钟形下游喷嘴对10~30 μm的粒子加速效果最好。当粉末在30 μm以上时,锥形下游喷嘴的加速效果最好。对于Al粉,当为下游220 mm长喷嘴时,钟形下游喷嘴对10~50 μm的粒子加速效果最好,喇叭形下游喷嘴加速效果最差。结论 冷喷涂喷嘴下游形状对气体与粒子加速有显著的影响。     

超音速等离子喷涂NiCr-Cr3C2工艺的参数优化

采用四因素三水平正交试验,通过在线监测喷涂粒子的温度和速度,对电流、电压、喷涂距离和主气流量四个超音速等离子喷涂的主要参数进行优化设计.结果表明:四个因素对喷涂粒子温度的影响均较大,电压和主气流量对喷涂粒子速度的影响较大;优化的工艺参数为电压150 V、电流400A、喷涂距离85 cm、氩气流量4.2m3/h,采用该优...     

WC-17Co 粉末尺寸对粒子飞行状态与涂层性能的影响分析

目的 提高碳化钨涂层的性能.方法 运用Fluent软件进行超音速火焰喷涂焰流的仿真模拟,得出喷涂距离-焰流速度、喷涂距离-焰流温度曲线.采用粒子飞行监测仪对三组不同粒度(粒子平均直径分别为21.72、32.92、42.56 μm)WC-17Co粉末在超音速火焰喷涂过程中的飞行状态进行监测,并得出喷涂距离-速度、喷涂距离-温度曲线,揭示喷涂过程中焰流速度、温度对粒子速度和温度的影响.通过扫描电镜观察分析不同粒度WC-17Co粉末撞击镍718合金基体后的扁平化程度,测量不同粒度WC-17Co涂层的孔隙率,比较涂层致密度的差异,同时采用压痕法测量涂层的硬度.结果 WC-17Co粒子飞行速度和温度随喷涂距离的增加呈先增大后减小的趋势,且粒子飞行速度和温度随粉末粒径的增大而减小,根据粉末粒径的不同,其速度峰值在690～810 m/s之间变化,温度峰值在1890～2050℃之间变化.直径越小的粒子撞击基体后的扁平率越高,扁平率在1.94～2.35之间.WC-17Co涂层的孔隙率随粒子直径的增大而升高,涂层的硬度与孔隙率成反比,涂层努氏硬度在1072～1284HK之间.结论 超音速火焰喷涂过程中,碳化钨粉末的飞行速度和温度呈先增大后减小的趋势,且飞行速度和温度与粒子直径大小成反比.碳化钨涂层的致密度与硬度随粒子直径的增大而减小.     

多功能超音速火焰喷涂粒子特性的数值模拟

通过建立多功能超音速火焰喷涂火焰流场的数值模型,对超音速火焰喷涂粒子的速度特性和温度特性进行数值模拟,其结果揭示了多功能超音速火焰喷涂粒子的速度和温度的变化规律.根据数值模拟结果分析了粉末粒度对火焰焰流速度和温度的影响,用不同粒度参数重复模拟计算,这对喷涂粉末的加速和加热性能具有重要意义.     

喷涂工艺参数对硅灰石涂层结构的影响

采用等离子喷涂方法,在不同喷涂距离、主气流量和喷涂功率下制备硅灰石涂层.使用扫描电镜观察了涂层的微观形貌,研究了喷涂工艺参数对涂层结构的影响.结果表明,在较大主气流量下,随着喷涂距离增加,涂层粒子扁平化程度降低,涂层内孔隙逐渐增多;在较小主气流量下,涂层粒子扁平化程度随喷涂距离增加呈现先增加后减小的趋势.主气流量增加,涂层致密,粒子扁平充分.喷涂功率增加,粒子熔化好,涂层致密;但随喷涂功率进一步增加,涂层中出现较多的圆形孔隙.喷涂工艺参数对涂层结构的影响主要通过影响熔融粒子的温度和速度所致.     

An Investigation on Powder Injection in the High-Pressure Cold Spray Process

High-pressure cold spray process is a relatively new coating process that uses high-velocity powder particles to form coatings. One of the requirements for this process is to inject the particles to be sprayed into a prenozzle chamber where both the particles and the powder feed gas are entrained into the primary gas stream. In this study, we investigated the effects of powder injection on coating formation through both experimental studies and computational simulations. Several issues related to powder injection will be examined, including the size of powder injector, the differential pressure, powder gas flow, and injector clogging. It is shown that an improved powder injector design not only enables the use of reduced amount of powder carrier gas flow but also maintains steady, clogging-free spraying conditions. Combining with properly selected injection conditions, it can also lead to enhanced coating deposition by kinetic spray process.     

Effect of Using Liquid Feedstock in a High Pressure Cold Spray Nozzle

This study investigates the effect of water injection in the high pressure chamber of a cold spray nozzle. A De Laval nozzle geometry with constant back pressure and temperature is modeled numerically using Reynolds Stress Model coupled equations. Water spray with a droplet size of 10-100 ??m is modeled using both uniform and Rosin-Rammler size distributions. The two-phase flow of gas-liquid is modeled using an unsteady discrete phase mass source with two-way coupling with the main gas flow. Upon injection, the droplets in the water spray evaporate while travelling through the nozzle due to momentum and energy exchange with the gas flow. The evaporation behavior in the presence of water content is modeled and a correlation between the initial diameter and the diameter just before the throat is obtained. As a result, the proper droplet size distribution with a fully evaporative spray can be used as a carrier of nano-particles in cold spray nozzles. Having the results, guides us to substitute the un-evaporated part of the droplet with an equal diameter agglomerate of nano-particles and find a minimum fraction of nano-particles suspended in the liquid which guarantees fully evaporative liquid spray injection.     

Particle behavior in supersonic flow during the cold spray process

The cold spray process is a relatively new process that uses high velocity metallic particles for surface modifications. Metallic powder particles are injected into a converging-diverging nozzle and accelerated to supersonic velocities. In this study two-dimensional temperature and velocitiy distributions of gas along the nozzle axis are calculated and the effects of gas pressure and temperature on particle velocities and temperature inside and outside the nozzle are investigated. It was found that acceleration of the gas velocity takes place in the area of the nozzle throat, and it increases and reaches a maximum value at the nozzle exit. Due to compression shocks, irregular changes of the gas jet properties were found in the area after the nozzle and these resulted in the experience of the maximum particle velocity by the change of the particle size at a given gas pressure and temperature.     

Particle-in-flight monitoring in thermal spray processes

A diagnostic system based on non-intensified CCD image sensor is applied for particle-in-flight monitoring of different deposition processes: cold gas dynamic spray (CGDS), computer-controlled detonation spray (CCDS) and direct metal deposition (DMD). An additional illumination source for measuring particle velocity in CGDS and DMD processes is used. Particle velocity measurements are carried out aiming optimization of a Cold Spray nozzle with two zones of powder injection for spaying Al powder. In a pulsed-periodic process like detonation spraying, particle-in-flight visualization and velocity measurements are done by synchronizing detonation pulses with the CCD-camera-based diagnostic tool. A significant variation of particles velocity along the detonation plume is observed. In DMD process, dependence between the carrier gas flow rate and particle velocity is found.     

Effect of the expansion ratio and length ratio on a gas-particle flow in a converging-diverging cold spray nozzle

A cold spray process is a relatively new process that uses high velocity metallic particles for surface modifications. Metallic powder particles are injected into a converging-diverging nozzle and accelerated to supersonic velocities. Gas accelerates in the throat of the nozzle and reaches a maximum speed at the nozzle exit. Due to compression shocks just outside the nozzle, the gas jet has an irregular shape. Experiments on the expansion ratio and the length ratio of the nozzle, particularly in terms of their relation to the gas pressure, temperature and nozzle length, were conducted for the purpose of reducing the shockwave [1].     

冷喷涂粒子速度-温度协同作用及复合喷涂新工艺研究进展

从冷喷涂粒子速度与温度协同问题出发,归纳总结了影响冷喷涂涂层质量的主要因素,并在此基础上,重点综述了喷嘴结构、气体类型与性质、粒子形态与材料等工艺参数与粒子速度-温度的作用关系.提高喷枪喷嘴扩张段膨胀比,改善黏性效应,提高高速区面积,使用高热扩散系数材料的喷嘴,均能够显著改善粒子速度-温度的协同效果.在工业应用中,可采用喷丸辅助冷喷涂、激光辅助冷喷涂、静电辅助冷喷涂、真空冷喷涂等新型复合沉积技术,实现高强低塑性喷涂粒子材料的沉积成形.最后,就如何深入研究速度-温度高质量协同并获得高质量涂层进行了展望.     

Numerical simulation on syphonage effect of laval nozzle for low pressure cold spray system

Instead of injected by high pressure powder feeder, powders can be drawn into the nozzle by syphonage effect generated by supersonic gas flow in low pressure cold spray. This characteristic makes low pressure cold spray conveniently for on-site operation. However, no data have ever been reported on the relationship between the nozzle structures and the gas flow in the powder feeder pipe. In this paper, a CFD software (STAR CCM+) was used to calculate the gas flow in nozzle of the DYMET 413 commercial low pressure cold spray system. Variation of structures and process parameters based on the commercial system were also investigated. The syphonage effect is strongly influenced by the powder feeding location, the temperature and pressure in prechamber has little effect on syphonage effect in powder feeder pipe. The syphonaged gas will decelerate the gas velocity and low down the gas temperature in nozzle, so it is best to control the mass flow rate of powder feeding gas by selecting the location. One of the disadvantages is that the particles will collide with the nozzle wall which makes the nozzle a short service life.     

An Investigation on Temperature Distribution Within the Substrate and Nozzle Wall in Cold Spraying by Numerical and Experimental Methods

During cold spraying (CS), heat exchange between the hot driving gas and the solid bodies, e.g., spray nozzle and substrate, results in the temperature redistribution within the solid bodies. In this study, numerical and experimental investigations on the heating behavior of the substrate and nozzle wall were conducted to clarify the temperature distribution within the solid bodies in CS. The results show that after heating by the hot gas, the highest temperature presents at the center point of the substrate and decreases toward the substrate back surface and edge. With increasing standoff distance or decreasing inlet temperature, the substrate temperature decreases gradually, but the temperature gradient within the substrate changes little. The numerical results are consistent with the experimental measurements. Besides, it is also found that increasing the substrate size (diameter) can lead to the gradual increment in the substrate temperature. Moreover, the numerical study on the temperature distribution within the nozzle wall reveals that the highest temperature presents at the throat section of the nozzle and that the nozzle material significantly affects the temperature distribution within the nozzle wall.