Plasma Spraying of Metal Coatings Using CO2-Based Gas Mixtures

Compared to argon, plasmas generated by molecular gases and operated at the same electric current level contain much higher enthalpy. This is because molecular gases must dissociate before ionization, which requires larger energy input. The authors have developed a new DC plasma torch, which operates with a mixture of carbon dioxide (CO2) and methane (CH4). The torch was employed for plasma spray coating with input power in a range of 30 to 45 kW. This paper reports on the effect of CO2/CH4 mixtures on the particle conditions during spraying of nickel alloy powders. Results of gas composition analysis at various distances from the nozzle exit are presented. The particle in-flight conditions, coating microstructure, and deposition efficiency are analyzed.