Microstructures and Properties of Nano-structural WC-12Co Coatings Deposited by AC-HVAF

WC-12Co powder with nano WC grains was used to deposit wear resistant coatings by AC-HVAF (acukote high velocity air-fuel) spray system. The phase compositions and microstructures of the coatings were examined. The microhardness, fracture toughness and wear resistance were investigated. According to the X-ray diffraction (XRD) analysis, the principal phase is WC, and its decomposition products are not found. The sprayed coating has a porosity lower than 1% and the grain sizes of coatings are among 80∼100 nm which contribute to an average microhardness (HV0.3) as high as 19 403 MPa on the surface and 17 410 MPa on the cross-section. At the load of 15 N and rotational speed of 1198 r/min of WC counter body, the nano-sized coatings show a decreased average mass loss by 40% compared with micro-sized coatings, and a stable friction coefficient of 0.26∼0.28 (micron-sized coatings: 0.25∼0.4) in the dry wear conditions. It is concluded that the sprayed nano structural WC-12Co coatings have a better wear resistance.