Microstructural and mechanical characterizations of a novel HVOF-sprayed WC-Co coating deposited from electroless Ni-P coated WC-12Co powders

In this research, a novel WC-Co coating was deposited from electroless Ni-P coated WC-12Co powders using high velocity oxygen fuel (HVOF) process. Toward this purpose, an electroless Ni-P plating process was used to develop a uniform Ni-P layer on the surface of WC-12Co powders. The obtained Ni-P coated powders were then used as HVOF feedstock material. Microstructural characteristics of the Ni-P coated WC-12Co powders and the resultant coating, which is denoted as Ni-P modified coating, were investigated using X-ray diffractometry (XRD) and high resolution field emission scanning electron microscopy (HR FE SEM). The micro-hardness, elastic modulus and fracture toughness measurements were executed to evaluate the mechanical properties of the Ni-P modified coating. For comparison, the same experiments were performed on two conventional HVOF sprayed WC-12Co and WC-17Co coatings. The Ni-P modified WC-12Co coating showed a dense structure with extremely low porosity of ∼0.3% which was much lower than that of WC-12Co and WC-17Co coatings. Besides, it was observed that the Ni-P modified coating has undergone negligible decarburization of 2.6% as compared to conventional WC-12Co and WC-17Co coatings with that of 16.3 and 17.6%. The Ni-P modified coating showed the maximum hardness of ∼11.45 GPa, while lower hardness values of 10.98 and 10.59 GPa were measured for the WC-12Co and WC-17Co coatings. The fracture toughness of Ni-P modified WC-12Co coating was found to be 9.86 MPa m1/2, indicating 71.2 and 61.1% increase in comparison with WC-12Co and WC-17Co coatings, respectively.