The Comparative Study of WC-Ni Coatings Deposited by APS and HV-APS Processes

This study investigates the properties of WC-10Ni cermet coatings deposited by plasma spraying using two different plasma torches: a conventional A60 torch (APS) and an advanced Axial III torch (HV-APS). The aim of the work was to compare the microstructure, porosity, surface roughness, phase composition, and mechanical properties (hardness and instrumented indentation), as well as erosion, scratch response, and resistance to tribological wear of the obtained coatings. The coatings were deposited onto S235 steel substrates using WC-10Ni (WOKA 3302) powder. The results revealed that both coatings exhibit a typical lamellar structure characteristic of plasma-sprayed materials; however, distinct differences in surface roughness, porosity, and mechanical response were observed. The coating produced using the Axial III torch showed lower porosity (~6%) and higher hardness (~1000 HV) compared to the coating deposited with the A60 torch (~12% porosity and ~831 HV). Phase analysis confirmed the presence of WC, W₂C, and Ni in both coatings, indicating partial decarburization of carbides during the spraying process. Erosion resistance tests did not reveal significant differences between the coatings. Erosion testing revealed comparable performance for both coatings, with erosion rates of approximately 0.7 mg/min. Scratch testing showed significantly lower acoustic emission activity for the Axial III coating, indicating less intensive fracture-related events during loading and confirming its more compact microstructure. In contrast, ball-on-disk tribological tests demonstrated comparable wear rates for both coatings (≈9 × 10^-5 mm³·N^-1·m^-1), despite the substantially higher hardness of the Axial III coating (1010 HV0.2 compared with 792 HV0.2 for the A60 coating). These results indicate that the improvements in hardness and coating densification achieved by the HV-APS process did not result in a measurable reduction in steady-state sliding wear under the applied test conditions.