Development and Characteristics of Long Laminar Plasma Jet to Spraying YSZ Coatings

A novel direct current non-transferred arc plasma torch that can generate silent (<80 dB), stable and super long laminar plasma jet (300 mm~720 mm) in ambient air is independently developed. The lengths of laminar plasma jet increase monotonically as the output power (8 kW~30 kW) and the gas flow rate (8 L/min~ 15 L/min, 70% N₂+30% Ar in volume) increase. The flow field characteristics and properties of plasma gas within this laminar plasma torch and the maintenance of long laminar plasma jet in atmosphere air is demonstrated by numerical simulation and experiment approach. Microstructures and properties of 8YSZ coatings under super long spraying distances ranging from 130 mm to 500 mm are discussed. The results show the refractory 8YSZ powder in this long laminar plasma jet can be melted sufficiently even up to the boiling point, a lot of vapor deposited areas can be found from the top and polished cross sections of coatings, although the stable output power of laminar plasma torch is only 25 kW ~26 kW (I=160 A, G=14 L/min) during spraying process. This may provide extensive options for different plasma spraying applications and fundamentally improve the plasma working environment of all workers.