Research Of Jet Characteristic And Drop Spreading Solidification Behavior In Plasma Spraying Process

Plasma spraying has a wide range of applications in petrochemical, modern industry and other fields. The present domestic simulation work is less about supersonic plasma spraying. The existing research focused on the low pressure environment. Most of the numerical simulation based on single temperature plasma model of local thermodynamic equilibrium. The chemical reaction, the change of specific heat, enthalpy, viscosity, thermophoresis force and pressure gradient force are ignored. Due to the plasma spraying process complex physical and chemical process, some basic mechanism is still not really clear, especially to the lack of understanding of plasma flame flow and particle interaction and molten drops spreading and solidification mechanism. The important research direction is the study of plasma spraying whole process.In order to further study of plasma spraying process, this paper study the flow field and temperature field in the inner powder form supersonic spray gun and the speed, heating process and broken refining behavior of powder particles using the method of numerical analysis combined with experimental. The dual temperature plasma model of local thermodynamic equilibrium is adopted. The chemical reaction, thermophoresis force and pressure gradient force are considered. The temperature and velocity of particle are monitored through the SprayWatch-2i to verify the accuracy of the numerical calculation results. Researches show that:Hydrogen gas can promote the temperature and velocity of the plasma spraying flow field. Temperature and velocity of jet flow field supersonic plasma spraying are much higher than normal atmospheric plasma spraying. Particles in the flow field of supersonic plasma spraying melting and refining more easily. Coating quality is best when spraying distance is 80 mm in atmospheric plasma spraying. Coating quality is best when spraying distance is 100 mm in supersonic atmospheric plasma spraying. Supersonic plasma coating porosity is lower than normal plasma spraying.The VOF method is applied to track the solidification process of molten drops of gas-liquid-solid interface. The special device is adopted to collect the colliding particles. The article morphology are observed through SEM and 3d laser microscope. The Reynolds number, the weber number and the number of Ohnesorge are characterized quantitatively to drip spreading and splash. Researches show that:Splash formed in the edge of the spreading along with the increase of droplet diameter and velocity. Along with the increase of Reynolds number, drop morphology will change from nosplash to splash. When oh> 0.2, the critical value for the splash is Re> 470±10. When oh< 0.2, the critical value for the splash is We>1.35 x 104±100.With the increase of the substrate surface roughness, a large number of holes appeared. Splash strengthen along with the increase of thermal contact resistance. The previous drop spreading hinde the behind drop from spreading. Solidification promotes for spreading flat rate. The relationship between flat rate and Reynolds number in SAPS approximately accord with liu model. The relationship between flat rate and Reynolds number in APS approximately accord with Yoshida model.LBM method is used to simulate the multicomponent mixture solidified growth behavior in supersonic plasma spraying process.The influence of forced convection on solidification growth is considered in simulation process. Researches show that:The up-flow grow fast and down-flow growth is restrained under the condition of considering convection. Under the big supercooling degree, grain boundary occur volatility and secondary dendrite growth happens. Plasma coating is in the columnar crystal shape under large temperature gradient. The Columnar crystal growth direction is toward to the positive temperature gradient. Influenced by convection, columnar crystals appear secondary dendrite growth. Upstream dendrite is developed and downstream dendritic growth is restrained.These studies could improve the understanding of the supersonic plasma spraying process and has guiding effect to a targeted optimization of process parameters. It has an important theoretical and practical significance to improve the level of industrialization of plasma spraying.