Mathematical modelling of Inconel 718 particles in HVOF thermal spraying S. Kamnis, S. Gu ⁎ , N. Zeoli School of Engineering Science, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom Received 21 June 2007; accepted in revised form 1 October 2007 Available online 16 October 2007 Abstract High velocity oxygen fuel (HVOF) thermal spray technology is able to produce very dense coating without over-heating powder particles. The quality of coating is directly related to the particle parameters such as velocity, temperature and state of melting or solidification. In order to obtain this particle data, mathematical models are developed to predict particle dynamic behaviour in a liquid fuelled high velocity oxy-fuel thermal spray gun. The particle transport equations are solved in a Lagrangian manner and coupled with the three-dimensional, chemically reacting, turbulent gas flow. The melting and solidification within particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight particle characteristics of Inconel 718 are studied and the effects of injection parameters on particle behavior are examined. The computational results show that the particles smaller than 10 μm undergo melting and solidification prior to impact while the particle larger than 20 μm never reach liquid state during the process. © 2007 Elsevier B.V. All rights reserved. Keywords: CFD; HVOF; Gas dynamics; Particle modeling 1. Introduction High velocity oxy-fuel (HVOF) thermal spraying offers a versatile technology to produce protective coatings, typically 200 to 500 μm thick, on the surfaces of engineering com- ponents. Materials being sprayed include metallic alloys, cer- mets, and polymers. In the HVOF process, oxygen and fuel are mixed and burnt in a combustion chamber at high flow rates (up to 1000 liter/min) and pressures (up to 12 bar) in order to produce a high-temperature (up to 3000 K), high-speed (up to 2000 m/s) gas jet. Powder particles, normally in the size range 5 to 65 μm, are injected into the gas jet so that they are heated and accelerated toward the substrate to be coated. On arrival at the substrate, particles are ideally in a melted or softened state and, on impact, form lenticular splats, which adhere well to the substrate and to one another. The HVOF gun is scanned cross the substrate to build up the required coating thickness in a number of passes. In HVOF spraying, the feedstock powder has density three or four orders of magnitude greater than the gas density; its other thermophysical properties are also significantly different from those of gas. A typical approach for modelling this multiphase flow is to treat gas and powder as separate gas and particle phases. The equations that describe the particle motion are solved in a Lagrangian frame and coupled with the Eulerian gas flow. The Euler–Lagrange approach has been used for the modeling of particle-gas interaction in various HVOF thermal spray systems [1–7]. However, most of the particle models are based on the gas fuelled HVOF systems [1–12] while the technology trend is moving towards high throughput liquid fuelled systems which have the advantage of using low cost fuel such as kerosene instead of propylene. The existing simulations on liquid fuelled HVOF guns are very limited. The early model from Yang et al. [13] is 2-dimensional which could not correctly represent the 3-dimensional design of gun and powder injection method. This paper reports the authors' continuation of research on liquid fuelled HVOF system from their latest work [14] which has shown 3-dimensional gas flow patterns of a kerosene burning gun. The purpose of this study is to examine particle motion and heat transfer within the gas flow field by invest- igating the effect of particle injection parameters. Available online at www.sciencedirect.com Surface & Coatings Technology 202 (2008) 2715 – 2724 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +44 23 8059 8520; fax: +44 23 8059 3230. E-mail addresses: kamniss@aston.ac.uk (S. Kamnis), s.gu@soton.ac.uk (S. Gu). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2007.10.006