Microstructure and wear resistance of spherical tungsten carbide rein-forced cobalt-based composite coating

In order to improve the wear resistance of EH40-C steel, four cobalt-based composite coatings containing 0%WC, 30%WC, 45%WC, and 60%WC were prepared on the surface by plasma transfer arc (PTA). The microstructure and phase of the four fabricated composite coatings were analyzed using scanning electron microscope (SEM) with energy spectrum analysis (EDS), and X-ray diffractometer (XRD). Subsequently, the friction and wear tests in a -10 degrees C simulated environment were carried out on a BRUKER UMT TriboLab. The wear depth and profile were determined with a noncontact 3D optical profilometer. The results reveal that coating structure of 0%WC+Co composed of network structure and sheet structure, coating structure of 30%WC+Co coating composed of dendritic structure and sheet structure. With the increase in the WC content, the dendritic structure will gradually grow up, and finally turn into fishbone structure. The microhardness of 0%WC+Co, 30%WC+Co, 45%WC+Co and 60%WC+Co coatings is 303 HV0.2, 411 HV0.2, 664 HV0.2 and 701 HV0.2. The wear resistance results indicate that addition of hard phase cast WC can effectively improve the wear resistance of the coating. However, when the content of WC is higher than 45%, the improvement of wear resistance is not obvious. Therefore, the optimum addition content of WC is 45%.