Abstract

The HVOF process is used for coating protective layers on surfaces exposed to corrosion and wear. This process involves a supersonic two-phase flow of gas-solid particles. The main objective of this thesis is to explore certain key factors that influence the process efficiency such as gas-particle interactions, particle in-flight conditions, and particle loading. To study the effect of gas-particles interactions, a Lagrangian approach which tracks individual particles in the continuous gas, is used. The supersonic gas flow leaving an HVOF nozzle is over-expanded and its adjustment to the atmospheric pressure results in shock diamonds formation, while flow impingement on a substrate results in bow-shock development. Both the shocks are responsible for affecting the particle conditions. The strength and location of bow shock vary for different substrate geometries and stand-off distances. In this work, various particle sizes impinging on different substrate configurations are simulated and the particle interactions with both the shocks are presented in detail. To find the effect of particle loading on the gas phase, a dense particulate phase scenario is assumed. A fully Eulerian approach, which treats the particles as a fluid, is used to simulate the HVOF process and the two-phase flow characteristics were investigated for various particle loadings. The particulate phase was found to be dense near the nozzle centerline and dilute near the wall. In the particle-dense region, the gas phase characteristics were found to be severely affected, which significantly affects the particle velocity