Modelling of plasma spraying of ceramic coatings at atmospheric pressure

Abstract

Abstract Many works have been devoted to the study of plasma sprayed coatings and, if progresses have been made, the coatings are still resulting more from an empirical understanding than from a scientific one. In this paper are presented what is the present state of our knowledge in the modelling and measurement of the parameters controlling the thermomechanical properties of coatings, especially: • - The influence of the way particulates flatten and splats are formed (with their fast temperature evolution upon impact), as well as the way the strands and passes thicknesses and temperature gradients within them are controlled. • - The influence of the injection velocity and size distribution of the particulates, as well as their morphology on the trajectory, velocity, diameter and surface temperature distributions upon impact. The modelling problems (steep temperature gradients, evaporation, non-continuum effects, heat propagation,…) are underlined as well as the comparison with measurements giving only mean statistical values. • - The influence of the development of the plasma column inside the arc chamber and nozzle, arc striking at the anode, surrounding atmosphere sucked down by the plasma jet… on the length and diameter of the plasma jets and the comparison of modelling with measurements (temperature through emission spectroscopy, velocity through LDA of small particles or fluctuations…) with emphasis on the difficulties which are still to be solved.