Melting/Oxidation Behavior of In-Flight Particles in Plasma Spray Processes

A comprehensive model describing the melting and oxidation of in-flight particles during plasma spray has been presented which includes the models for heat, momentum and mass transfer of carrier gas, and particle heating, acceleration and evaporation. The effect of evaporation-induced mass transfer on heat flux to the particle surface has been taken into consideration along with the effect of oxidation-induced evaporation due to the production of volatile oxides on the particle surface, and effects of variable plasma properties and non-continuum effects under plasma conditions. Computational results on molybdenum and zirconium particles in an argon-hydrogen DC plasma spray system have been obtained and discussed. The temperature and melting formation of particles with different sizes along their trajectories are depicted as well as other particle parameters such as velocity, evaporation rate and oxide content, which manifests that the behavior of particles are diverse due to particle size distribution in the spray coating operation. The effects of gun power on the heating, acceleration, melting, evaporation and oxidation of particles have also been discussed.