A proposed process control chart for DC plasma spraying process. Part II. Experimental verification for spraying alumina

The role of particle injection velocity in influencing the nature of alumin a coatings obtained by plasma spraying was studied. Previously reported pro cess chart obtained by computational fluid dynamics (CFD) study on the part icle states of alumina with respect to particle injection velocity and size was verified experimentally. For this purpose, alumina particles of three different size ranges with a mean size of 25, 40, and 76 mum were subjected to different injection velocities. The coating obtained was analyzed for c ross-sectional microstructure and thickness by optical microscopy. In addit ion, the role of particle injection velocity and size in influencing the co ating-deposition efficiency was studied. The experimental results agreed we ll with the CFD results, which had indicated the dependence of particle tra jectory in the plasma plume on the particle injection velocity and size lea ding to the changes in the extent of melting, While a higher coating thickn ess and deposition efficiency was obtained with 25-mum particles, with furt her increase in particle size, a reverse trend, was observed. This was attr ibuted to the changes in heat-transfer characteristics of the particles wit h size, which governed the coating buildup and deposition efficiency.