Influence of the Injector Head Geometry on the Particle Injection in Plasma Spraying

Abstract

In plasma spraying, the particle velocity at the injector outlet has significant influence on the particles’ penetration into the plasma jet. The geometry of the injector and the flow rate of the carrier gas determine the particle velocities. Based on numerical simulations, it is evident that higher particle velocities and thus, a deeper penetration of the particles into the plasma jet, can be realized with an injector geometry which is significantly longer than the standard injector. This results in a higher melting degree of the particles, especially for operating parameters leading to high-speed plasma jets. In order to verify the results of the simulations, injectors with different diameters and lengths were manufactured and their influence on the particle velocities at the injector outlet was measured via particle diagnostics. The injectors were furthermore used to apply alumina coatings with a multi-cathode plasma generator. The resulting coating thicknesses were determined. Based on these results, it seems feasible to influence the injection behavior of the particles positively by increasing the injector length. By comparing the relative intensities of the α- and γ-alumina peaks in the XRD patterns, it is shown that these changes in injector geometry did not affect the phase composition.