Numerical Simulation Of Plasma Spray Coating Surface Morphology And Residual Stress

lasma spraying coating is one of the widely used techniques in thermal spraying,it can effectively improve wear resist,high temperature resist etc.,and have greatly increased the life expectancy of parts.In the process of spraying,due to differences of substrate surface roughnesses,substrate temperatures,environmental pressures and speeds of molten drop,they have a great i MPact on the surface morphology of coating,these factors will make large influence of residual stress because of the larger temperature gradient and differences in physical characteristics between substrate and coating,the life expectancy of parts is seriously affected leading to fracture,buckling,spalling,and delamination.Therefore,there is great significance in studying effect of process parameters on plasma spray coating surface morphology and residual stress.By using fluid mechanics software-Fluent,a three-dimensional computational model of splats formation includes heat transfer and solidificaion is establishe,the governing equations are discretized according to typical finite volume conventions,a volume of fluid tracking algorithm is used to rack the droplet free surface.It was simulated that a molten droplet was impacting,spreading,heat conducting,solidification,and forming the process of splat on the steel substrate,by analyzing at differences of substrate surface roughnesses,substrate temperatures,environmental pressures and speeds of molten drop,they had a great impact on the surface morphology of layers;on the basis of above,and it continued to put the second drop to impact the solidified layer,so the coatings were forming,further illustrating that the factors affected the coatings surface morphology and residual stress.The simulation of splat formation indicated:Substrate roughnesses are appropriately increscent,the thickness of layer is more uniform and the surface morphology is better,the final morphology shape is thin and the other side is thich;substrate temperatures are appropriately increscent,the gas is more advantageous to let out,and the pores are reduced in the layers,the spreading thickness of layer is decreasd gradually with the increase of temperature,and the spreading radius are gradually increasing,the morphology of sediment is more close to the disc;with the reduce of the environment pressure,the sediment of disc shape are more and more,the sediments of edge are almost no splash,the pores are reduced;the speeds of molten drop are appropriately increscent,the scope of layer morphology is more and more big,the sputtering shapes of edge are more and bigger,the speed is too low or too high,it will lead to increase the pore.The final morphology of coating and residual stress indicated:Under the low pressure,the range of forming coating is bigger than the obtained coating under the high pressure,but the thickness is just opposite,and thinner,with the increase of environmental pressure,the bond strength of coating is increscent;when the speed of molten drop isincrescent,the spreading diameter of coating is larger and the thickness is reduced,the axial maximum compressive stress is increased with the increase of the speed of molten drop;when substrate temperature rises,the final morphology of coating is thick and the middle is thin,but the density of coating on the central is enhanced constantly,the pores are lower;with the increase of roughness,the "wall" in the edge of sediment is more and more thin,the pores are reduced,all of the coating edges are almost no splash.Substrate temperature and the surface roughness of substrate should exist an optimal range,it will ensure that the coating and substrate have a better bonding strength.