Influence of Fuel/Oxygen ratio on coating properties and cavitation resistance of WC and Cr3C2 cermet coatings deposited by HVOF

Hydraulic turbines are strongly affected by cavitation, which damages the surface and can change the original profile. The study of thermal spray processes and materials becomes relevant to improve surface properties and cavitation resistance of turbines. The main objective of this work is to evaluate the influence of the Fuel/oxygen ratio on the HVOF deposition of WC–20Cr₃C₂-7Ni and Cr₃C₂-37WC-18M coatings. The velocity and temperature of the particles were measured, as well as the coatings properties as hardness, porosity and cavitation resistance were evaluated. The HVOF F/O ratio was performed at two different levels, 0.33 and 0.43, using Kerosene as liquid fuel. The samples with the lowest cavitation resistance were the alloys deposited with the lower fuel ratio, which also showed lower micro-hardness and higher value of porosity. The samples with the better cavitation resistance were deposited with higher F/O ratio. The wear mechanism started with the nucleation of the cavitation that occurred in the pores forming craters and the detachment of the lamellae was also observed, indicated by the smoothness of the surface. The results show that, regardless of the coating material, the total ratio level had significant influence on cavitation resistance of these materials.