Microstructure and Tribological Properties of Laser-Remelted Ni-Based WC Coatings Obtained by Plasma Spraying

Ni-based WC coatings were successfully fabricated on Ti6Al4V titanium alloy substrate by the air plasma spraying (APS) process. The as-sprayed coatings were remelted with a continuous wave CO2 laser. The coatings were characterized using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), an X-ray diffractometer (XRD), a Vickers microhardness tester, a ball-on-disc friction and wear tester, and a 3D measuring laser microscope. The results indicated that the laser-remelted coatings possessed a more homogeneous microstructure and lower porosity, were more dense, and bonded well with the substrate. The lamellar structure and microcracks of the as-sprayed coatings were eliminated after laser remelting. The average porosity markedly decreased to 1.3% from 9.7% of the as-sprayed coating. Many needle dendrites grew outward from the dissolution surface of the WC, while massive precipitates abundantly appeared around and away from the WC particles. The microhardness of the laser-remelted coating was enhanced to 884.7–1363.3 HV0.3, which was much higher than that of the as-sprayed coatings and nearly three times higher than that of the substrate. Under the same load, the wear volume of the substrate was nearly 13 times higher than that of the laser-remelted coating and five times higher than that of the as-sprayed coating. The wear mechanism of the laser-remelted coating and the as-sprayed coating was mainly abrasive wear; however, the wear mechanisms of the substrate were a combination of adhesive wear, micro-cutting, and delamination wear.