High-velocity Oxygen-fuel Spraying Research Articles

Interaction of particles with carrier gas in HVOF spraying systems

Several designs of high-velocity oxygen fuel (HVOF) thermal spray systems have been created during the last decade. The most advanced systems are now producing coatings comparable in quality to detonation (D-gun) coatings. This paper presents numerical analysis of the interaction of dispersive particles with the carrying gas flow for three different HVOF systems, along with a method to calculate the parameters of sprayed particles that highlights the advantages and limitations of each design. The method includes gas dynamical calculations of the gas flow in an accelerating channel and calculations of the injected par-motion and thermal state (temperature and melted mass fraction). The calculations were performed for particles of tungsten carbide, aluminum oxide, and zirconium oxide with size distributions of 10 to 80 μm. Two conventional types of HVOF systems were considered: those with a supersonic accelerating channel and those with a subsonic accelerating channel (without a de Laval nozzle). A novel design is pro-posed that contains a combined gas dynamical path with functionally separated regions of heating and acceleration. The regularities and distinctions in the behavior of the metallic and ceramic oxide particles are discussed for different jet configurations. The results obtained indicate that it is possible to signifi-cantly affect particle parameters by using the new configuration solutions without creating construction complications.

WC-NiCr溶射皮膜の硬さと耐摩耗性に及ぼす熱処理の影響

The effect of heat treatment on hardness and wear resistance of WC-27%NiCr sprayed coating on SUS403 made by High Velocity Oxygen Fuel Spraying (HVOF) has been studied to improve abrasive wear resistance.Specimens were heated to either 573, 673 and 773 K and held at those temperature for various times, up to 45 h. The change in micro-vickers hardness (load 2.94 N) after heat treatment was measured after the samples coold to room temperature. The wear rate of the specimens against α-SiC with the plane-on-plane contact pressure of 0.196 MPa, in water suspending 9 mass% silica powder were measured by a sliding velocity of 0.5 m/s.The results obtained are as follows:(1) Heat treatment increased the hardness of WC-27%NiCr sprayed coatings.(2) The increase of the hardness due to heat treatment was dependent on the void decreasing of the sprayed coatings.(3) The wear rate of the heated WC-27%NiCr sprayed coatings in water suspending silica powder became triple increment against that of the coating before heating.