Microstructure and properties of high velocity oxygen fuel sprayed (WC-Co)-Ni coatings

Abstract

The (WC-Co)-Ni composite coatings were fabricated by high velocity oxygen fuel (HVOF) spraying process using (WC-Co)-Ni powders prepared through blending agglomerated WC-Co powder with Ni powder. Microstructure and phase composition of the coatings deposited with different content of Ni powders were characterized using scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. The microhardness, elastic modulus and fracture toughness of the coatings were tested by indentation method. The wear properties of the coatings sliding in dry and wet conditions as well as under different applied loads were tested using a modified pin-on-disc tester. Experimental results showed that the microstructure of HVOF sprayed (WC-Co)-Ni composite coating was exhibited some lamella features consisted of deformed WC-Co splats and even distributed Ni splats, which was significantly influenced by the Ni content in original powders. Phase constitutions of the coatings mainly consisted of WC, W2C, Co, Ni and a little of Co6W6C, which were related to the Ni content in original powders. Microhardness, elastic modulus, fracture toughness and wear rate of the coatings were varied from 435.5 ± 34.7 to 708.7 ± 43.3 Hv0.3, from 58.9 ± 10.3 to 135.0 ± 82.7 GPa from 1.07 ± 0.11 to 2.41 ± 0.09 MPa m1/2 and from 0.15 to 0.4 mg•(Nm)−1, respectively. The abrasive wear of the coating occurred mainly in the form of gouging and peeling off in addition to a little of plastic deformation.