Effect of WC–Co content on the microstructure and properties of NiCrBSi composite coatings fabricated by supersonic plasma spraying

This paper presents our detailed investigation into the effect of the WC–Co content on the microstructure and properties of supersonic plasma sprayed NiCrBSi composite coatings on Inconel 718. The results showed that the NiCrBSi/WC–Co composite consisted predominantly of Ni, Ni₃Fe, Ni₃B, CrB, WC, Cr₇C₃, and WFeB₂, in addition to lesser amounts of W₂C, Cr₃Ni₂Si, and Co₃B. The coating containing 15 wt% WC–Co exhibited the most compact microstructure with the lowest number of defects, as well as the lowest porosity (i.e., 0.6%). The mechanical properties of the as-sprayed coatings were significantly enhanced by the addition of WC–Co. Upon increasing the WC–Co content, the friction coefficients of the as-sprayed coatings increased from 0.59 to 0.74. The main wear mechanisms transformed from abrasive wear coupled with spallation for the NiCrBSi coatings with a low WC–Co content to adhesive wear and fatigue fracture for coatings with a medium WC–Co content, to a combination of brittle fracture failure and slight abrasive wear for coatings with a high WC–Co content. Furthermore, the coating with 15 wt% WC–Co registered a higher microhardness (910.6 HV) and adhesive strength (44.7 MPa), and a lower wear rate (8 × 10⁻⁶mm³/(N m)) than the other as-sprayed coatings, indicating that this was the optimal WC–Co content for this type of NiCrBSi-based composite coating on Inconel 718. The synergy between the compact structure, higher microhardness, and adhesive strength was considered responsible for the excellent wear resistance of the NiCrBSi–based composite coating with a WC–Co content of 15 wt%.