Plume-Targeted Cooling Effects for High- and Medium-Density Metals Fabricated by Controlled Atmosphere Plasma Spray

Thermal spray processes benefit from workpiece cooling to prevent overheating of the substrate, retain metallurgical properties (e.g., temper), and control the thermal component of residual stresses.Cold-gas "plume quenching" is a plume-targeting cooling technique, where an argon jet is directed perpendicularly to the plasma jet and far enough downstream that most particle heating and acceleration is complete.The intent is to redicret the high-temperature plasma gases away from the substrate without impacting particle temperature and velocity.However, there has been little investigation of its effect on molten particles in the plume and the resulting coating properties.This study examines high-and medium-density tantalum and nickel coatings, fabricated with Controlled Atmosphere Plasma Spray with and without the addition of plume quenching on aluminum and titanium substrates.To observe the direct effects of plume quenching on the plume, Differential Flame Thermometry was used to examine substrate temperature and plume spot size.To compare the effect of plume quenching on coating deposition, the deposition efficiency was calculated through coating mass gain, and the coating density, stiffness, adhesion, and residual stresses were measured.Tantalum and nickel coatings were largely unaffected by plume quenching with respect to deposition efficiencies, coating density, adhesion and stiffness, plume quenching generally reduced residual stress amongst most substrate-coating pairings.These results indicate that a plume quench can be used without affecting the coating properties for high-and medium-density metals while providing the benefits of substrate cooling that increases with higher plume quench gas flow rates.