| 摘要: |
| 热喷涂技术是表面工程领域中极为重要的一种装备强化修复技术，其中以气体放电形式为热源的喷涂技术包括等离子喷涂和电弧喷涂，两者更是占据热喷涂领域的绝大市场份额，采用数值模拟可以解决一些在试验上较为棘手的重点研究问题， 如等离子体流场和熔滴传热传质行为等，以期实现工艺参数的准确调控和优异涂层的制备。研究电弧及等离子喷涂模拟的模型差异化问题及流场速度、温度、电磁性质，归纳相关模拟的发展历程，并调查试验与模拟的吻合程度。结果表明：电弧喷涂中丝材原料会使阴阳极产生温度差，水平速度分布较发散，熔滴模型也多未考虑熔滴群间相互作用；等离子喷涂研究中常用的三维瞬态双温模型已十分贴近实际工况，对熔滴飞行中的加热、加速过程及破碎行为的研究已较为完备，但仍存在湍流模型计算精度不够、对鞘层弧柱区的研究不够深入等问题。后续应重点在电弧喷涂多液滴模型、等离子体电磁作用和等离子丝材喷涂工艺的数值模拟等方面进行深入研究。 |
| 关键词: 放电 等离子喷涂 数值分析 射流 |
| DOI：10.11933/j.issn.1007-9289.20230129001 |
| 分类号:TG174 |
| 基金项目:国家自然科学基金（52105235，52130509，52075542）； 173 基金（B04011）资助项目 |
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| Research Status on Numerical Simulation of Spraying with Gas Discharge Heat Source |
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LI Tianhao1,2, HUANG Yanfei2, LIU Ming2, BAI Yu1, WANG Haidou2,3, MA Guozheng2, GUO Weiling2
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1.State Key Lab for Mechanical Behavior of Materials, Xi’ an Jiaotong University, Xi’ an 710049 , China;2.National Key Laboratory for Remanufacturing, Army Academy of Armored Forces, Beijing 100072 , China;3.National Engineering Research Center for Remanufacturing, Army Academy of Armored Forces,Beijing 100072 , China
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| Abstract: |
| Gas discharge generates the arc or plasma that acts as a heat source. Arc spraying and plasma spraying using the generated energy as a heat source are collectively called gas discharge heat source spraying. When spraying occurs, the arc or plasma discharge combined with the carrier gas excites the jet with high-temperature and high-speed plasma, which melts the powder or wire material; finally, the molten droplet is deposited on a substrate to form a coating. Notably, various interactions occur between the jet and molten droplets during the in-flight process, such as melting and fragmentation of the droplets and the drag effect between the droplet and jet. However, real-time monitoring of the jet and molten droplets is difficult owing to the high temperature and harsh environment during the spraying process. As an emerging computational method, numerical simulation can be used to study the transient the field and the physical behavior of molten droplets during the spraying process; thus, numerical simulation is an important tool and area of focus. In this study, the differences and potential drawbacks of models in the simulation of two spraying processes, arc spraying and plasma spraying, are studied, and the characteristic distribution of different jets, state of the droplets, and mechanisms of acceleration and heating of in-flight molten droplets are investigated. In the arc spraying process, wire materials with different thermal conductivities cause the static temperature at the cathode to be much higher than that at the anode, and the velocity distribution of the jet flow is more diffused in the wire plane. The use of a massive wire can increase the velocity and temperature of the molten droplets; however, this might exacerbate asymmetric melting of the wire. Therefore, core wires are expected to be more promising for future applications. Most models consider the interaction of the individual droplets and jet flow instead of droplet groups, and the improved two-fluid model does not consider the thermophoretic force; therefore, further adjustments and advanced models are required. Plasma spraying has been more extensively studied than arc spraying. This study focuses on the following key scientific issues in the spraying process before coating deposition: On one hand, the energy source used for plasma spraying, excitation, and plasma flow directly affect the state of the materials. Thus, determining an appropriate turbulence model based on the flow state is the first important issue. The plasma two-temperature model using the non-local thermal equilibrium very closely reflects the actual working conditions and has become the most suitable base model because the electromagnetic processes at the cathode and anode crucially affect plasma formation and the plasma characteristics, thereby affecting the electromagnetic properties of the cathode / anode and sheath regions, such as the arc reattachment behavior and anode wear. The physical parameters of in-flight molten droplets have been evaluated in several studies using theoretical analyses, experimental demonstrations, and numerical simulations. The effects of various process parameters were analyzed, providing an effective guide for achieving the desired experimental results and for determining the optimal parameters. Finally, the mass and heat transfer processes in molten droplets in the jet flow were systematically analyzed. For example, the droplet goes through the following stages: acceleration and heating, constant temperature and velocity, deceleration and cooling in the jet flow, and fragmentation via vibration breaking as the main mechanism. However, numerical simulations still have limitations such as insufficient simulation accuracy and a lack of in-depth research. Future research on multi-droplets modeling of arc spraying, simulation of the turbulence and electromagnetic properties of plasma spraying, and numerical simulation of plasma transfer arc spraying, a new technique that is becoming increasingly mature, can potentially provide directives for advancing the simulation of gas discharge heat source spraying. This study summarizes the evolution of each physical process model in the numerical simulation of gas discharge heat source spraying since the emergence of thermal spraying simulation, and provides theoretical guidance for the experiments by combining the results of each stage of evolution. |
| Key words: discharge plasma spraying numerical analysis jet |
