Strengthening Mechanism and Properties of Co-WC Composite Coatings Deposited by PTAW

Cobalt (Co)-based tungsten carbide (WC) wear-resistant coatings with different content of WC were prepared on the surface of Q235 low carbon steel by plasma-transferred arc welding. The properties of the coatings such as strengthening mechanism, microhardness and wear properties were tested by using a metallurgical microscope, scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, Rockwell hardness tester, and friction wear equipment. The results show that the main reasons for the strengthening of spray welding layer are the solution strengthening formed by alpha-Co with supersaturated tungsten (W) and the dispersion strengthening caused by eutectic precipitated carbide and silicide. The proportion of the solid solution of W in alpha-Co steadily ranges from 18.00 to 19.59%. The morphologies of rich W-phase are mainly related to the content of W. With the content of W increasing, the evolution process of the shape is the amorphous form -> damascene shape -> star-like shape -> the polygon. Amorphous W-rich phase can be obtained when the content of WC ranges from 20 to 30%, evenly distributed W-rich phase in the shape of damascene or star can be obtained when the WC content ranges from 30 to 40%, and the polygonal W-rich phase can be obtained at the percentage of 40-50%.