材料期刊网

目的 真空度直接影响着真空冷喷涂时气体流动特性和颗粒撞击速度,研究真空度对气体和颗粒流动特性的影响. 方法 确定真空冷喷涂系统结构,采用FLUENT软件进行真空冷喷涂气固两相流研究,通过数值模拟研究真空度对流场和颗粒撞击速度的影响,并研究相同压力比下的气固两相流特性.结果 当入口压力一定时,喷管内的气体轴线速度、密度和温度与环境压力大小无关;而在射流区,环境压力越小,则气体轴线速度波动越小、密度越低,但到达基板后的气体温度均接近喷管入口温度. 环境压力对大粒径颗粒的撞击速度影响较大,颗粒撞击速度随环境压力增大而先增后减,最佳环境压力可根据气相云图和气体密度来确定. 当进出口压力比相同时,喷管内和射流区域内的气相速度云图基本相同,气体轴线速度曲线基本重合,而基板前的颗粒速度不同,此时环境压力越低,颗粒速度越高,越有利于形成涂层. 结论 采用计算流体动力学分析方法厘清了真空度对真空冷喷涂气固两相流的影响,为涂层制备奠定了理论基础.

Objective The flow behavior of gas and the particle impact velocity are directly affected by the vacuum degree in the process of vacuum cold spray. The influences of vacuum degree on gas and particle flow properties were studied. Methods The structure of the vacuum cold spray system was determined, and the gas-solid flow in vacuum spray was studied based on FLUENT. The influences of vacuum degree on the flow field and particle impact velocity were explored through numerical simulation, and the gas-solid flow properties under the same pressure ratio were studied. Results The numerical research indicated that when the inlet pressure was constant, the axis velocity, the density and the temperature of gas in the nozzle were independent of the ambient pres-sure, whereas in the jet flow region, lower ambient pressure led to lower fluctuation of the gas velocities and lower gas density. However, when the gas reached the substrate, its temperature was close to the inlet temperature in all cases. The ambient pressure had obvious effect on the impact velocity of the particle with large diameter, and the impact velocity first increased and then de-creased with increasing ambient pressure, and the optimal ambient pressure could be determined by the gas contour and its density.When the pressure ratios of the inlet and outlet of the nozzle were the same, the gas contours in the nozzle and the jet flow region were almost the same, and the curves of the gas axis velocities almost coincided. While the particle velocities before the substrate were different, the lower the ambient pressure, the higher the particle velocity, which was more beneficial to coating formation. Conclusion The influence of vacuum degree on the gas-solid flow in vacuum spray was clarified based on the CFD, which laid the ground work for the preparation of coating.