Microstructure refinement and alloying of WC-CoCr coatings by electron beam treatment

The corrosion and wear behaviour of HVOF (high velocity oxygen fuel) sprayed WC-CoCr (cermet) coatings were investigated before and after electron beam (EB) remelting. In this regard, the coatings were deposited on INCONEL 617 substrate. The mentioned Ni-based alloy is well known for its good corrosion behaviour in chloride containing media but exhibits not enough good wear properties.The paper investigates the influence of EB-remelting process on sliding wear respectively on corrosion resistance in 1 M NaCl solution of the alloyed surface. Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) were performed before respectively after the EB-treatment in order to investigate the coating morphology as well as the phase modification achieved through the alloying process. Tribological tests concerning the sliding wear behaviour of the tested materials revealed a significant decrease of the wear rate for both the as-sprayed coating respectively the alloyed surface in comparison with the base material. However, the as-sprayed cermet coating exhibits the lowest wear rate among the investigated samples.The microhardness of the alloyed surface was higher (1100 HV₀₃) in comparison with that of the as-sprayed cermet coating (905 HV₀₃) as a result of new phase formation (especially the η-Co₄W₂C). The corrosion behaviour in salt water of the EB remelted surface was also considerably improved in contrast to the as-sprayed cermet coating.