An Investigation of Particle Injection and Resulting In-Flight Particle Behavior During Air Plasma Spraying

Abstract

In this article we present our studies on the role of particle injection on the in-flight particle characteristics in an external orthogonally injected air plasma spray system. The influence of carrier gas on the in-flight particle state has been investigated, experimentally and using simulation, for Yttria Stabilized Zirconia (YSZ) thermal spray powder processed in an Ar-H2 plasma. Diagnostic tools such as IPP and SPT have been used to measure the plume characteristics and ensemble temperature while DPV-2000 has been used to measure the distributions of individual particle characteristics such as temperature, velocity and size, at the point of the maximum particle flux and at various points (square grid) in the plume cross-section. Three-dimensional simulations have been performed for the cases presented in the experiments. Specifically, the effects of carrier gas flow rate on the in-flight particle characteristics were studied at multiple stand-off distances. Simulation results agree well with the experimental observation that the particle velocity and temperature will increase with the plume angle and then decrease after reaching a maxima for a given process parameter combination and stand-off distance. This maxima has been observed at the same plume angle for different process parameter combinations. The results of this study are currently being used to 'optimize' the particle injection and trajectory, which enables better understanding of the influence of plasma forming and stabilizing parameters (gas flows and arc current) on the in-flight particle behavior.