Abstract
Thermal spraying of a nanograined WC-12Co cermet powder using high velocity oxy-fuel was employed to produce nanostructured coatings. The spray conditions were varied by employing a wide range of thermal spray parameter settings and using either hydrogen or propylene as fuel gas. By determining the characteristics of the spray jet for each set of spray conditions and by studying various aspects of the coatings, including the microstructure, properties, and performance in dry abrasion tests, conclusions were drawn regarding the effect of the spray parameters on the properties and performance. When comparing the effect of using hydrogen or propylene as fuel on in-flight particle characteristics, the results indicated that, for a given particle temperature, the particle velocity tended to be higher with hydrogen than propylene. As well, it was found that the coatings produced using hydrogen tended to have a higher microhardness and a lesser degree of carbide degradation. The resistance to wear in dry abrasion was significantly higher for coatings produced using hydrogen as fuel. For both series of coatings, it was found that the abrasion resistance increased with the particle temperature at the point of impact during thermal spraying and with the hardness of the coating. The abrasion resistance of coatings produced using propylene appeared to be much more sensitive to changes in hardness. For the thermal spray system studied in this work, the results indicate that nanostructured WC-12Co coatings having a maximum abrasion resistance are obtained by using hydrogen as fuel under conditions such that the particles achieve temperatures above approximately 1850-1900°C and a speed greater than 575-600 m/s.
