Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions
Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions
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DOI：
10.3390/coatings11060726
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发表时间：
2021-06
期刊：
影响因子：
3.4
通讯作者：
Tao Zhang;G. Mariaux;A. Vardelle;Chang-Jiu Li
中科院分区：
文献类型：
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作者：
Tao Zhang;G. Mariaux;A. Vardelle;Chang-Jiu Li
等离子体喷涂-物理气相沉积（PS-PVD）是一种用于沉积均匀和大面积涂层的新兴技术。由于等离子体射流的特性难以在整个燃烧室中测量，计算流体动力学（CFD）模拟可以预测等离子体射流的温度场、速度场和压力场。然而，由于PS-PVD通常在低于500 Pa的压力下运行，因此基于连续假设的计算流体动力学预测的有效性存在问题。本研究针对PS-PVD系统进行了CFD模拟，该系统采用低功率（<50 kW）的氩-氢等离子体射流或高功率（≥50 kW）的氩-氦等离子体射流运行。系统地研究了净电弧功率和燃烧室压力对等离子体射流特性和局部梯度克努森数（Kn）的影响。Kn被发现是低于0.2，除了在对应于第一膨胀冲击波的区域。随着电弧净功率的增加，该区域的峰值迅速减小，随着沉积室压力的增加，该区域的宽度减小。基于研究结果，局部努森数被引入检测条件下连续的方法是有效的PS-PVD条件下的第一次和CFD模拟可以合理地用于确定本研究的条件下的工艺参数窗口。
Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study.