Microstructure and properties of Ni-Co-TiN composite coatings prepared on the surface of stubble cutters

In order to improve surface hardness and corrosion resistance of stubble cutters, and then to extend their service life, the Ni-Co-TiN composite coatings were prepared by ultrasonic-assisted jet electrodeposition on the surface of 45 steel used in stubble cutters. The optimal process parameters for producing Ni-Co-TiN coatings were determined by orthogonal experiment. The microstructure, surface morphology,phase structure and elemental composition of the coatings were observed by scanning electron microscope（SEM）, transmission electron microscopy（TEM）, X-ray diffractometer（XRD） and energy dispersive spectrometer（EDS）, respectively. Moreover, the microhardness and corrosion resistance of coatings were tested by microhardness tester and electrochemical workstation. The orthogonal experiment results demonstrated that the optimal process parameters for producing Ni-Co-TiN coatings were listed as follows, the jet speed of the plating solution 4 m/s, the ultrasonic power 120 W, the content of TiN nanoparticles 10 g/L and the electrode spacing of 8 mm. The nickel grain sizes of the Ni-Co-TiN coating prepared with the optimal process parameters were obviously refined and TiN particles were dispersed in the coating. The microhardness of the coating was as high as 489. 82 HV, the self-corrosion potential（E_corr） was-0. 342 V and self-corrosion current density（I_corr） was 2. 15×10^-6 A/cm².