Theoretical Investigations on Sprayed Particle-Plasma Interactions to Optimize Processing Parameters in D.C. Thermal Plasma Spraying

Abstract

A numerical model is proposed to simulate the behavior of particles injected into a dc spraying plasma in conjunction with the code that calculates the plasma jet characteristics. The sprayed particle-plasma interaction, particle loading effect and the particle internal heat transfer including phase transformations are considered together in the model to present a realistic prediction for the characteristic features of plasma spraying. The temperature and velocity fields in a plasma jet expanding region outside the nozzle are found by a pre-developed code based on the arc-gas interactions inside the nozzle depending on the operating conditions of the torch. The influence of particle injection on the plasma jet characteristics is treated as the source in the fluid equations governing the plasma jet in semi-three dimensional calculations caused by non-axisymmetric injection of powders. The calculated velocity profiles of powder particles along the axial distance are compared with those obtained from experiments, and the determination of optimal spraying conditions are discussed from the results calculated from the present model. This model gives more realistic information for plasma spraying than earlier works which have not included the loading effects and non-axisymmetric injection of powders in dc thermal plasma spraying. The theoretical predictions of the sprayed particle characteristics using this model can be helpful for determining preliminary range and optimal values of operating parameters for plasma spray processes.