Numerical modelling of in-flight particle dynamics of non-spherical powder

Abstract

High velocity oxygen fuel (HVOF) is an important thermal spraying technology in depositing high quality coatings. Its ability to produce high particle velocities and relatively low particle temperatures is its most salient feature. Several computational fluid dynamic (CFD) models have been developed to study the in-flight particle behavior during thermal spraying. These models are limited to spherical particles, which are only appropriate for modelling gas atomised powders. On the other hand, hardmetal powders such as WC-Co are created using high energy ball milling and are not normally spherical. To examine the effect of particle morphology on particle dynamics, mathematical models are developed in the present paper to predict the in-flight particle behavior in a liquid fuelled HVOF thermal spray gun. The particle transport equations are coupled with the three-dimensional, chemically reacting, turbulent gas flow, and solved in a Lagrangian manner. The melting and solidification within the particles as a result of heat exchange with the surrounding gas flow are solved numerically. The results demonstrate that non-spherical particles gain more momentum and less heat during the HVOF process than spherical particles. Non-spherical particles are also predicted to stay closer to the center of the gas jet than spherical particles.