In this research, a low cost high-velocity air-fuel (HVAF) system was developed and applied for thermal spraying of WC-Co coatings. The resulting coatings were evaluated using optical and scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers microhardness measurements. The quality of sprayed WC-Co coatings shows that the developed HVAF system can be an alternative to the existing HVOF with substantial savings on operating costs.

Thermo-abrasive blasting is a technique, which combines conventional abrasive blasting and HVAF processes to prepare surfaces prior coating. Thermo-abrasive blasting has a number of advantages over conventional abrasive blasting as the result of a higher nozzle pressure and heat, which helps to remove impurities from the surface. However, practice showed that the short life of blasting nozzles due to thermal stresses and excessive wear is the biggest drawback of this method. Therefore, the correct nozzle geometry and suitable materials are critical for an efficient operation of thermo-abrasive blasting systems. In this study, computational fluid dynamics and finite element analyses were used to obtain the temperature distribution and to evaluate thermal stresses in nozzle materials. The materials investigated include tungsten carbide-cobalt (WC-6wt.% Co), hot pressed dense silicon carbide (SiC) and SiALON (Si 3 N 4 -Al 2 O 3 -AlN). The analysis and experiments showed that WC-CO nozzles produce the best overall results of thermal shock resistance and wear in thermo-abrasive blasting.

In the last few years, a new method for surface preparation has evolved, namely thermo-abrasive blasting. This technique utilises a high enthalpy thermal jet to propel abrasive particles. The thermo-abrasive blasting gun, also called a thermal gun, is based on the principles of High Velocity Air Fuel (HVAF) processes. Some empirical data is available on thermo-abrasive blasting method and systems. To effectively improve on nozzle design and productivity, modelling of the thermo-abrasive blasting process was required. This paper describes the computational modelling of the thermal gun with computational fluid dynamic software, namely STAR-CD. The developed computational model can be applied to HVAF systems used for thermo-abrasive blasting and thermal spraying.