Microstructure and Cavitation Erosion Resistance of HVOF Deposited WC-Co Coatings with Different Sized WC

Abstract

Conventional, multimodal and nanostructured WC-12Co coatings with different WC sizes and distributions were prepared by high velocity oxy-fuel spray (HVOF). The micrographs and structures of the coatings were analyzed by scanning electron microscope (SEM), X-ray diffractometer (XRD) et al. The porosity, microhardness and fracture toughness of the WC-Co coatings were measured. The coating resistance to cavitation erosion (CE) was investigated by ultrasonic vibration cavitation equipment and the cavitation mechanisms were explored. Results show that there is serious WC decarburization in nanostructured and multimodal WC-Co coatings with the formation of W2C and W phases. The nanostructured WC-Co coating has the densest microstructure with lowest porosity compared to the other two WC-Co coatings, as well as the highest fracture toughness among the three coatings. It was also discovered that the nanostructured WC-Co coating exhibits the best CE resistance and that the CE rate is approximately one-third in comparison with conventional coating.

Effects of Cobalt Content on the Microstructure, Mechanical Properties and Cavitation Erosion Resistance of HVOF Sprayed Coatings

“…On the other hand, the size of the WC particles in the WC-17Co coating was uniform and smaller than the WC-12Co coating. Some studies [11,18] have indicated that a smaller WC particle size is desirable in decreasing porosity.…”

“…To improve the CE resistance of material, high-velocity air fuel [7], high-velocity oxygen fuel (HVOF) [8], arc spraying [9], atmospheric plasma spraying [10], and other surface modification technologies had been developed. Due to the optimal combination of mechanical strength (hardness and fracture toughness), HVOF-sprayed WC-Co-based ceramic-metal (cermet) composites coatings can improve CE resistance [11,12]. Lamana et al [13] demonstrated that an increase in Co content could lead to an increase in the fracture toughness and CE resistance of WC-Co coatings, which also resulted from the increase in compressive residual stress.…”

Effect of Nitrogen Ion Implantation on the Cavitation Erosion Resistance and Cobalt-Based Solid Solution Phase Transformations of HIPed Stellite 6

“…Cobalt based materials are among the most cavitation erosion-resistant materials commercially available and chemical composition of Stellite 6 alloy exhibits excellent cavitation erosion (CE) resistance. Therefore, Stellite 6 superior CE behaviour is documented by many scientific papers, for the stellites produced as alloy weld overlays [17], plasma transferred arc (PTA) overlay welding [18], laser cladding [11], shielded metal arc welding (SMAW) [19] and also HVOF deposited Stellite 6 coatings [20] and cobalt-based WC-Co cermet's deposits [21][22][23]. Unfortunately, as far as the authors' knowledge no paper describes cavitation properties of the powder metallurgy satellites and analysis its cavitation wear behaviour of HIPed Stellite 6.…”

Mechanical Properties of Cobalt-based Alloy Coating Applied Using High-velocity Oxygen Gas and Liquid Fuel Spraying Processes

“…Compared with atmospheric plasma spraying, the molten powder particles in HVOF are faster, have higher momentum and lower temperature, and do not evaporate when they hit the substrate, so the HVOF spraying process is suitable for achieving superhard alloy coatings. (8)(9)(10)(11)(12) This deposition process has little environmental impact and is regarded as the most promising substitute for hard chrome plating; indeed, the US Federal Aviation Administration has approved this process for spraying many parts of aircraft engines. (13) The temperature generated by HVOF spraying can reach 2000-3000 ℃.…”