The Deposition Behavior Of Plasma Sprayed Cast Iron Splat On Soft Metal Substrates

Producing wear-resistant coatings on soft metal materials can greatly increase their application space and service time.The lower cost of gray cast iron and the self-lubricating effect of graphite,as well as the high efficiency and flexibility of plasma spraying technology,resulting in its an effective method to improve the wear resistance of soft metal surfaces by using plasma spray technology to prepare the gray cast iron coating.The adhesion of coating is determining whether the coating is detached or not.Based on the formation and structural characteristics of the thermal spray coating,the microstructure and properties of the coating are mainly affected by the deposition behavior of the individual particles,namely the morphology of splats,the bonding of splat-substrate and the bonding of inter-splats.In the present study,individual cast iron splat was deposited on polished aluminum,brass,magnesium alloy surface by atmospheric plasma spraying technique(APS).The effects of the arc power,spray distance,and substrate preheating temperature on the morphology of the splat and splat-substrate bonding were studied.Moreover,the heat transfer process between the splat and the substrate was studied by a numerical calculation method to elucidate the formation mechanisms of the morphology and the splat-substrate bonding.Main research results are summarized as follows:1.The study of the morphology of cast iron splats shows that:(1)Cast iron splats deposited on aluminum substrates show most of the splats are splashing when the temperature of the aluminum substrate is room temperature;however,when the initial temperature of the aluminum substrate increases to 150°C,most of the splats are disc-shaped;continuing to increase the substrate preheat temperature to 300 °C,star-shaped splash-like splats form.(2)When the brass substrate temperature is 25°C,all the cast iron splats are donut-shaped;when the temperature of the substrate rises to 150°C,about 80% of the splats appear to be ray-like splashes.While continuing to raise the initial temperature of the substrate to 300°C,92% of the splats are approximately disc-shaped.(3)When the magnesium alloy substrate temperature is 25°C,most of the splats show an irregular splash morphology.When the temperature rises to 150°C,about 65% of splats are centered in depression morphology,and some of the particles show petal morphology;the substrate temperature is 300?,about 85% of the splats exhibited a layered spreading morphology,while other particles showed a disk-like morphology.2.Combine the particle cross-sectional photos and the grain size of the sprayed particles observed by the AFM to calculate the contact resistance of the droplet-substrate interface,establish a two-dimensional heat transfer model considering the actual thermal resistance and phase transition,and calculate the droplet through finite element calculations.With the temperature change of the substrate and the integrated EDS and blade-hot-setting results,the study of the particle-matrix bonding interface structure shows that:(1)When the initial temperature of the aluminum substrate is at room temperature,the bonding performance between the splat and substrate is weak;When the substrate preheating temperature rises above 150°C,the bonding between the splat and the substrate is improved.When the substrate is preheated to 300°C,obvious plastic deformation and depression occur on the surface of the substrate.At the same time,barbs appear at the edges of the splats.The donding of the splatsubstrate has been further improved.(2)When the magnesium alloy substrate temperature is 25°C,the bonding of splat-substrate is mainly mechanically bonded;when the substrate is preheated to 150°C,the maximum depth of the substrate is 5.1±0.2 ?m;when the substrate is preheated to 300?,the maximum depth increased to 6.2 ± 0.1?m,and the bonding performance was further strengthened.(3)When the brass substrate is preheated from room temperature to 300°C,the mechanical bonding between the splat and substrate is dominant,and the bonding performance is poor.