Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates

This paper investigates WC-10Co4Cr coatings on 4340 steel prepared by conventional HVOF and novel cold spraying (CS) under optimal process parameters to address low wear resistance. The results show that the CS WC-10Co4Cr coating porosity is less than 0.1%, while the HVOF WC-10Co4Cr coating porosity is about 0.3%. The WC phase in the CS coating did not change, whereas the WC phase in the HVOF coating underwent decarburization and a new W2C phase was formed. The microhardness of the CS WC-10Co4Cr coating reaches 1617.2 HV0.3, which is about 50% higher than that of HVOF WC-10Co4Cr coating of 1061.3 HV0.3. The sliding wear rate of the CS WC-10Co4Cr coatings is 0.17 × 10−5 μm3/N·m, which is 40% of that of the HVOF coatings. The CS coating’s fretting wear rate is 1.28 μm3/N·m, which is 40% faster than that of HVOF coating. However, the bond strength of the CS WC-10Co4Cr coating (35 MPa) is lower than that of the HVOF coating (73.5 MPa). Overall, the WC-10Co4Cr coatings prepared by the CS process have higher hardness, denser coating microstructure, and better sliding wear resistance than those prepared by the conventional HVOF process.