Numerical Modeling of In-Flight Molten Metal Droplet Dynamics and Particle Oxidation in Atmospheric Plasma Spraying

Abstract

In Atmospheric Plasma Spraying (APS), it is important to understand the controlling factors dominating molten metal droplets’ reaction dynamics to control final coating compositions and properties. The present paper focuses on a novel Computational Fluid Dynamics (CFD) modeling of mass transfer mechanisms of an inflight molten metal droplet leading to droplet oxidation control during APS. The onset conditions of droplet internal circulation and its effect on the deoxidizer oxidation behavior during APS are theoretically examined. Moreover, rapidly supplying these elements from the inside to the droplet surface requires the rapid switching of the mass transfer mechanism to rapid convective flow due to a very limited in-flight time of less than 1ms. The temperature and velocity variations within the droplet would influence the thermo-physical properties of the droplet and the plasma gas and it controls the onset of the internal circulations within the droplets. A novel User Defined Function (UDF) is developed to capture the onset of Hill’s vortex formation and its effect on the rapid-rate convective mass transfer mechanism during APS. Further, a detailed analysis of particle size effect on in-flight in-situ deoxidation during APS of NiAlC droplets was performed. It is observed that the smaller size droplets will undergo more severe oxidation during a flight than larger size droplets due to more molecules of O2 available for reaction in the smaller droplet.