Numerical Study to Examine the Effect of Porosity on In-Flight Particle Dynamics
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JTTEE5 20:630–637 DOI: 10.1007/s11666-010-9606-9 1059-9630/$19.00 ASM International
Numerical Study to Examine the Effect of Porosity on In-Flight Particle Dynamics S. Kamnis, S. Gu, and M. Vardavoulias (Submitted September 14, 2010; in revised form November 9, 2010) High velocity oxygen fuel (HVOF) thermal spray has been widely used to deposit hard composite materials such as WC-Co powders for wear-resistant applications. Powder morphology varies according to production methods while new powder manufacturing techniques produce porous powders containing air voids which are not interconnected. The porous microstructure within the powder will influence in-flight thermal and aerodynamic behavior of particles which is expected to be different from fully solid powder. This article is devoted to study the heat and momentum transfer in a HVOF sprayed WC-Co particles with different sizes and porosity levels. The results highlight the importance of thermal gradients inside the particles as a result of microporosity and how HVOF operating parameters need to be modified considering such temperature gradient.
Keywords
CFD, HVOF, in-flight, porous powder, WC-Co
1. Introduction High velocity oxygen fuel (HVOF) thermal spraying has been applied successfully in producing coatings with higher density, superior bond strengths, and less decarburization due to its unique output of high particle velocities and relatively low particle temperatures. In the HVOF process, oxygen and fuel are mixed and burnt in a combustion chamber at high flow rates (up to 1000 L/min) and pressures (up to 12 bar) to produce a hot high-speed gas jet. Powder particles, normally in the size range 5-65 lm, are injected into the gas jet where they are heated and accelerated toward the substrate. On impact the particles 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. The impingement and deformation of thermally sprayed particles have been investigated using CFD (Ref 1-3) and FEA (Ref 4-6) methods. Numerical models have also been developed to study the in-flight particle behavior during thermal spraying. Euler-Lagrange method is the most widely adopted approach for modelling of particle-gas interaction in various HVOF thermal spray systems. In the material aspects, there is a growing interest in deposition of WC-Co materials. As a class of hard S. Kamnis and M. Vardavoulias, PyroGenesis S.A., Technological Park of Lavrio, 19500 Lavrio, Greece; S. Gu, School of Engineering Science, University of Southampton, Highfield, Southampton SO17 1BJ, UK; and S. Gu, Department of Civil Engineering, Xian Jiaotong-Liverpool University, No.111 Renai Road, Suzhou Dushu Lake Higher Education Town, Suzhou 215123, Jiangsu Province, China. Contact e-mails: s.gu@soton. ac.uk and [email protected].
630—Volume 20(3) March 2011
List of Symbols
CD Cp D dp FD f h Hsf kg kp ks kc Pr Re St r T TL TS Tk T up ug
Drag coefficient Particle sp
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