A TORCH NOZZLE DESIGN TO IMPROVE PLASMA SPRAYING TECHNIQUES

The effects of nozzle design on the plasma characteristics of superson ic Row conditions are investigated using a D.C. plasma jet under low-p ressure plasma spraying conditions. Comparison is made between a 5 mm I.D. standard nozzle and a 13 mm E.D. (exit diameter) Mach 3 Laval noz zle. Emission spectroscopy is used to study the temperature and electr on density distributions in the plasma jets produced by the different nozzle configurations. The effects of the observed modifications of th e temperature and electron density fields on the properties of the pla sma sprayed deposits are studied using Rene 80 powders which are spray ed using both types of nozzle under similar operating conditions. The results show that the M3 Laval nozzle provides a better spraying effic iency and spraying density than a standard anode nozzle under similar conditions.