Abstract
Four high velocity thermal spray guns were evaluated in the production of 10%Co-4%Cr tungsten carbide cermets. Three HVOF guns (the JP-5000, JP-5000ST and DJ-2700) and one plasma gun, (the Mettech Axial III) were used to spray the same angular, agglomerated and crushed WC-10Co-4Cr powder. The DPV-2000 was used to monitor the in-flight velocity and temperature of the WC cermet sprayed particles. From those values, spray conditions were selected to produce coatings that were evaluated in terms of porosity, hardness and deposition efficiency. Results show that the plasma Axial III provides the highest particle temperature, between 2000°C and 2600°C, depending on the spray conditions. The JP-5000 imparts the highest velocity to the particles, between 550 m/s and 700 m/s, depending on the spray conditions. The ST version of the JP-5000 provides the same velocity as the standard version but with lower particle temperature. The DJ-2700 sprays particles with temperature and velocity between those of the JP5000 and the Mettech Axial III. Minimum porosity values of 2.1%, 3.7% and 5.3%) were obtained for the JP-5000, the DJ-2700 and the Axial III guns respectively. The porosity and carbide degradation are found to mostly depend on the particle velocity and temperature respectively. The values for the Vickers microhardness number (200g) ranged from 950 to 1250. Measurements of the deposition efficiency indicated a variation between 10 and 80%o, depending on the spray conditions and the gun used.
Influence of particle temperature and velocity on the microstructure and mechanical behaviour of high velocity oxy-fuel (HVOF)-sprayed nanostructured titania coatings
