Microstructure-property relations in WC-Co coatings sprayed from combinatorial Ni-plated and nanostructured powders

- In case of mc-WC coating, W2C precipitated as irregular fringes onto pre-existing WC.
- As for nc-WC coating, rounded W2C independently precipitated from W-rich Co matrix.
- Amorphous W-rich Co formed upon HVOF was more brittle than crystalline W-depleted Co.
- Ni-plated powders showed 66 and 85% drop in carbon loss relative to mc- and nc-WC.
- Ni/nc-WC coating exhibited the highest hardness (1168 Hv) and KIC (10.32 MPa·m1/2).

In this study, we addressed the effects of Ni-plating and nanostructuring of WC-Co powders on the microstructure-property relations and WC decarburization of WC-Co composite coatings. By high velocity oxygen fuel (HVOF) spraying, the coating materials were produced from four different powders, referred to as microstructured WC-Co (mc-WC), nanostructured WC-Co (nc-WC), Ni-plated microstructured WC-Co (Ni/mc-WC) and Ni-plated nanostructured WC-Co (Ni/nc-WC). We found that the coatings, deposited from Ni-free powders, undergo a high level of decarburization, thereby yielding W2C phase formation in brittle amorphous W-rich Co matrix that could be preferential site for crack propagation. On the contrary, the Ni-plating treatment could reduce the amount of decarburization of the coatings, resulting in the uniform distribution of WC phase in the W-depleted Co matrix. Consequently, we revealed the underlying mechanisms responsible for WC decarburization in the coatings, and further suggested that the coating deposited from Ni-plated and nanostructured powders exhibits a superior combination of hardness and fracture toughness as compared to other coatings.