The splat is the fundamental unit of thermally sprayed coatings,which has been one of the hottest issues for decades.In order to study the splat formation,an experiment was designed and conducted,in which a millimeter-size nickel metal droplet fell freely and impacted on aluminum and stainless steel substrate.The microstructural characteristics of the splat and the heat conduction and solidification processes during the flattening process have been studied numerically and experimentally.The effect of the droplet temperature,impact velocity as well as the substrate temperature was investigated.The phenomenon of substrate melting was observed after the spreading of nickel droplet,which became more pronounced when the initial substrate temperature increased.Increasing the impact velocity of droplet resulted in a decrease in the interfacial temperature between droplet and substrate. The splat is the fundamental unit of thermally sprayed coatings, which has been one of the hottest issues for decades.In order to study the splat formation, an experiment was designed and conducted, in which a millimeter-size nickel metal droplet fell freely and impacted on aluminum and stainless steel substrate. microstructural characteristics of the splat and the heat conduction and solidification processes during the flattening process have been studied numerically and experimentally. The effect of the droplet temperature, impact velocity as well as the substrate temperature was investigated. phenomenon of substrate melting was observed after the spreading of nickel droplet, which became more pronounced when the initial substrate temperature increased.Increasing the impact velocity of droplet resulted in a decrease in the interfacial temperature between droplet and substrate.