Experimental testing of a curvilinear gas shroud nozzle for improved plasma spraying

The performance of a new gas shroud nozzle attachment for plasma spraying w as rested experimentally using particle diagnostics, flow visualization, ar m coating characterization techniques. ii nozzle attachment with curvilinea r inner walls was tested and compared with a commercially available conical nozzle. Particle temperatures were measured with a high-speed ratio pyrome ter and particle velocities were measured with an intensified camera and a two-laser illumination system. Flow visualization,vas performed by seeding the surrounding air with smoke. Particle temperatures at the spraying dista nce were 300 K higher with the curvilinear insert. The plasma jet was narro wer but the particle velocity distribution at the spraying distance was unc hanged. Higher temperatures and improved particle melting with the curvilin ear insert resulted in a reduction in coating porosity (from 7.0 to 7.2 to 4.5-5.1%) and an increase in coating adhesion strength (from 27.2 to 42 MPa ), Shrouding as injected through a circular slot around tire nozzle exit wa s also seen to provide better protection than gas injected with the standar d sixteen-port configuration.