Effect of Spray Distance on the Microstructure and Corrosion Resistance of WC-based Coatings Sprayed by HVOF

Cermet coatings provide protection against an aggressive operating environment of machine and device elements, such as corrosion, wear or high-temperature conditions. Currently, WC-based cermet coatings are frequently used in different industry branches. In this work, conventional WC-based powders (WC-Co and WC-Co-Cr) were sprayed with high velocity oxy fuel (HVOF) onto AZ31 magnesium alloy with different spray distances (320 and 400 mm). The research aimed to investigate the effect of the spray distance on the microstructure of the coatings, phase composition and electrochemical corrosion resistance. Results revealed that a higher spray distance results in greater porosity, 1.9% and 2.3% for 320 mm and 2.8% and 3.1% for 400 mm in the case of WC-Co and WC-Co-Cr coatings, respectively. Also, an impact on coatings microhardness was observed, c.a. 1300 HV0.3 for shorter spray distances, whereas for longer ones it was less than 1100 HV0.3. The corrosion resistance estimated in potentiodynamic polarization measurements was the best for WC-Co-Cr coating deposited from the shorter spray distance, corrosion current density was equal to 2.9 mu A center dot cm-2 and polarization resistance was equal to 8424 omega center dot cm2.