Synthesis of nanostructured WC-12 pct Co coating using mechanical milling and high velocity oxygen fuel thermal spraying

A nanostructured WC-12 pet Co coating was synthesized using mechanical mill ing and high velocity oxygen fuel (HVOF) thermal spraying. The variation of powder characteristics with milling time and the performance of the coatin gs were investigated using scanning electron microscope (SEM), X-ray, trans mission electron microscope (TEM), thermogravimetric analyzer (TGA), and mi crohardness measurements. There is no evidence that indicates the presence of an amorphous phase in the sintered WC-12 pet Co powder, and the binder p hase in this powder is still crystalline Co. Mechanical milling of up to 20 hours did not lead to the formation of an amorphous phase in the sintered WC-12 pet Co powder. During the initial stages of the milling, the brittle carbide particles were first fractured into fragments and then embedded int o the binder phase. This process gradually formed polycrystal nanocomposite powders of the Co binder phase and W carbide particles. The conventional c old welding and fracturing processes primarily occurred among the Co binder powders and polycrystal composite powders. The nanostructured WC-12 pet Co coatings, synthesized in the present study, consist of an amorphous matrix and carbides with an average particle diameter of 35 nm. The coating posse sses an average microhardness of 1135 HV and higher resistance to indentati on fracture than that of its conventional counterpart.