Improvement of thermally sprayed WC-Co/NiCr coatings by surface laser processing

The present work deals with the post-treatment of thermally-sprayed WC–Co/NiCr coatings deposited by (High Velocity Oxygen Fuel) HVOF on a cylindrical substrate in AA 6082 T6 aluminium alloy with a High Power Diode Laser (HPDL). Laser operational parameters, especially laser power and scan rate, were investigated to find the best settings to improve the mechanical response of the WC–Co/NiCr coatings, preventing the onset of surface damage. Visual appearance and morphology of the coatings were investigated by contact gauge profilometry and scanning electron microscopy. The material microstructure was studied by combined scanning electron microscopy and energy dispersive X-ray spectroscopy. Hardness and wear resistance were analysed by instrumented indentation tests. Appropriate combinations of laser parameters were found to enhance significantly the mechanical performance of the WC–Co/NiCr coatings, whose structure was dense, compact and uniform, with hardness and wear endurance highly improved. In contrast, extreme irradiation densities of the laser beam should be carefully avoided to reduce the onset of defectiveness as wide fractures and/or additional porosities inside the thermally sprayed material.