Abstract:Owing to the arc ignition in twin wire arc spraying (TWAS) the wire tips are heated in three different zones. The outer part of the wire tips (contact zone) is heated directly by the arc ignition (zone I). The wires material in this zone becomes fully liquefied. The heat propagation phenomenon rises the temperature of the area immediately adjacent (towards the fed wires) generating a doughy material (zone II). Next to the doughy zone (towards the fed wires) the transferred heat softens the wire material causing a permanent deformation (zone III).
The deformation is due to the exerted aerodynamic forces of the atomization gas pressure. A high speed imaging system was used to observe the melting behavior, metal break up, and particle formation under different operating conditions. The liquidus metal in zone I is directly atomized in the form of smaller droplets. Their size is a function of the specific properties of the molten metal and the exerting aerodynamic forces. The doughy area (zone II) is the origin of the extruded metal sheets at the anode and cathode side. The extruded metal sheets in case of cored wires are shorter than the ones observed by solid wires. The extruded metal sheets support the re-ignition of the arc and therefore enhance the process stability in twin wire arc spraying. In this study the effects of adjustable parameters and powder filling on melting behavior, particle formation and process instability were revealed and a comparison between solid and cored wires was made. The findings can improve the accuracy of the TWAS process modeling and enhance the atomization of metal droplets through the adaption of specific nozzle geometry modification.
Keyword:Cored Wires；Arc Spraying；Instability
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