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

The plasma energy input rate of a de Ar + H-2 plasma jet has been measured experimentally under a series of vacuum plasma spraying (VPS) processing conditions. The plasma energy input rate increased approximately linearly with increasing plasma current and Ar flow rate, increased approximately parabolically with increasing H-2 flow rate, but did not vary measurably with changes in VPS chamber pressure. Based on these experimental results, an approximate analytical model has been developed to calculate the initial plasma gas temperature, degrees of Ar and ii ionization and the plasma gas velocity at the plasma gun exit as functions of the VPS processing parameters of plasma current, Ar flow rate, H-2 flow rate and chamber pressure. The model is based on an energy balance in the plasma gas between the input electrical energy and the energy consumed by gas dissociation, ionization and heating. In part II of this paper, the model is used to predict the boundary conditions for a subsequent computational fluid dynamics model of plasma gas and particle flow during VPS