Modelling and experimental analysis of vacuum plasma spraying.Part I: prediction of initial plasma properties at plasma gunexit

Abstract

The plasma energy input rate of a dc Ar + H2 plasma jet has been measuredexperimentally under a series of vacuum plasma spraying (VPS) processingconditions. The plasma energy input rate increased approximately linearly withincreasing plasma current and Ar flow rate, increased approximatelyparabolically with increasing H2 flow rate, but did not vary measurably withchanges in VPS chamber pressure. Based on these experimental results, anapproximate analytical model has been developed to calculate the initialplasma gas temperature, degrees of Ar and H ionization and the plasma gasvelocity at the plasma gun exit as functions of the VPS processing parametersof plasma current, Ar flow rate, H2 flow rate and chamber pressure. The modelis based on an energy balance in the plasma gas between the input electricalenergy and the energy consumed by gas dissociation, ionization and heating. Inpart II of this paper, the model is used to predict the boundary conditions for asubsequent computational fluid dynamics model of plasma gas and particle flowduring VPS.