Influence of the arc Chamber Design and of the Surrounding Atmosphere on the Characteristics and Temperature Distributions of Ar-H2 and Ar-He Spraying Plasma Jets

Abstract

The key parameters controlling the thermomechanical properties of plasma sprayed coatings (d.c. plasma spraying) are the heat and momentum transfers between the plasma jets and the injected particles. These, beside the particles size and injection velocity distributions as well as the plasma gas nature, depend strongly on the plasma isotherms lengths and diameters which in turn are controlled by nozzle, arc chamber and plasma gas injector designs. This paper is devoted to the study of these last parameters for Ar-H 2 and Ar-He plasma jets flowing in air or in controlled atmosphere chambers filled, at atmospheric pressure, with nitrogen or argon. After a brief description of the working principle of d.c. spraying plasma torches (thoriated tungsten cathode, stick type) and of the experimental set ups (automatized emission spectroscopy and energy balance of the plasma torch) are presented successively the influence of: - the gas injection close to the cathode tip on the plasma jet behaviour - the gas injector design on the plasma jet isotherms lengths and diameters - the gas nature (Ar-H 2 or Ar-He) and the surrounding atmosphere on the same parameters.