Direct current plasma spraying: Diagnostics and process simulation

This paper presents our current knowledge in direct current (d.c.) plasma spraying with conventional stick-type cathode plasma torches. It deals with the experimental methods and models used to better understand and/or control the characteristics of plasma jet, particles in-flight and at impact. The first part refers to measurements and on-line monitoring or control. The emphasis is on (i) the effect of arc root fluctuations and electrode wear on particle treatment and coating formation; (ii) the drastic a importance of the interface between the flattening particles and substrate. The second part examines the models used to predict gas flow field and particle parameter distributions at impact. It presents: (i) steady and 2-D models that allow optimal experimental design with a limited number of experiments I as well as education and training; (ii) 3-D and time dependent models that make it possible to take account of the arc root fluctuation at the anode and a stochastic and time-dependent particle injection description.