高速低温喷涂气固作用行为及喷涂系统研究进展

Progress of Gas-solid Interaction Behavior and Spray System of High Velocity Low Temperature Spray

高速低温喷涂是利用固相或含固相的低温粉末在高速度、高动能作用下碰撞基体表面沉积的喷涂方法,具有氧化轻微、结合牢固、组织致密、综合力学性能优异等潜在优势,在高性能金属或金属基复合材料涂层制备、增材制造和零件损伤修复等领域获得广泛关注。以粉末低温高速碰撞沉积过程为主线,凝练现有冷喷涂和低温超音速火焰喷涂两种具体工艺的共性特征,阐明喷涂气流与粉末颗粒的气固两相交互作用规律,分析出合理调控颗粒温度和速度是改善沉积体性能的关键。其次分析高速低温喷涂设备系统的构成,详细讨论各核心部件的结构设计策略及对气固流动行为的影响,总结出通过调整工艺参数与喷枪结构,可以实现颗粒温度和速度的按需控制。最后,对高速低温喷涂工艺及设备系统发展目前尚存的关键问题进行展望。总结如何通过喷涂参数与装置设计,最终达成调控沉积体性能的目的,有助于深入理解高速低温喷涂的沉积机理,对研制高性能的喷涂设备系统具有参考意义。

High-velocity low-temperature spray is a spray method that utilizes a solid-phase powder or a low-temperature powder containing a non-solid phase to deposit on a substrate surface through collision at high velocity and kinetic energy.Compared to the traditional thermal spray that relies on melting particles for coating deposition,this spray method exhibits potential advantages,such as low oxidation of the material,high bonding strength with the substrate,dense microstructure,and excellent comprehensive mechanical properties.Therefore,it has attracted extensive attention domestically and internationally in the fields of metal or metal matrix composite coatings,additive manufacturing,and the rapid repair of damaged components.First,as typical high-velocity low-temperature spray methods,cold spray,and low-temperature high-velocity oxygen-fuel spray share common characteristics:powder particles interact with the gas in the nozzle,experiencing heating and acceleration through heat transfer and the drag force of the gas.The elevated kinetic and internal energies of the particles may induce certain behaviors that have the potential to enhance interface bonding.These behaviors include fragmentation of the oxidation films,structural changes,and even localized melting upon collision with the material surface.The analysis of some studies indicates a significant influence of velocity and temperature on the material deposition behavior and the final coating performance.Subsequently,spray strategy planning and coating performance modulation can be performed,guided by the deposition window constrained by the particle velocity and temperature.The particle temperature determines the ductility during collision,thereby influencing the deformation behavior,surface morphology,flatness,material jetting behavior,and bonding quality,whereas the velocity determines the kinetic energy during collision,thereby influencing the stress and strain inside the material.The subsequent section of this paper discusses the composition of high-velocity low-temperature spray equipment systems,including the spray gun system(comprising a nozzle and gas heater),powder feeder,gas/fuel sources,spray scanning component,and control system.The structural design strategies of each major component and their influence on the gas-solid flow behavior are discussed in detail.The spray gun is the core component of the spray system,which comprises a nozzle that supplies initial kinetic energy to the gas and a gas heater that supplies initial internal energy to the gas.Under specific process conditions,the particle velocity demonstrates an initial increase followed by a decrease with the expansion length or expansion ratio of the nozzle,whereas the trend of the particle temperature is reversed.Gas heaters are primarily categorized as electric and combustion flame heaters.This serves as a crucial basis for distinguishing between cold spray and high-velocity oxygen-fuel spray.Electric heaters operate at a maximum temperature of approximately 1300 K and are designed with intricate and convoluted airflow paths within limited volumes to maximize heating efficiency.The maximum temperature of the combustion flame can reach 3400 K.Adjusting the type and proportion of combustion reactants,along with implementing rational cooling flow control strategies,allows for the continuous regulation of the flame temperature across a wide range.Therefore,a comprehensive approach involving the adjustment of the process parameters and spray gun structure achieves on-demand control of the particle temperature and velocity.Finally,some key issues in the high-velocity low-temperature spray process,and equipment systems are discussed.The main emphasis of this paper is to summarize the methods by which control over coating performance can be attained through the design of the spraying parameters and apparatus.This study contributes to an in-depth understanding of the deposition mechanisms in high-velocity low-temperature sprays and provides a valuable reference for the development of high-performance spray equipment systems.