In order to improve the mechanical properties of 40Cr steel, a Ni/Co - TiN nanocoating was prepared on its surface by ultrasonic jet electrodeposition. The surface morphology, phase structure and elemental composition of the coating were observed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and x - ray diffractometer (XRD). Moreover, the microhardness, wear resistance and corrosion resistance of coating were tested by microhardness tester, friction and wear tester and electrochemical workstation. Results showed that the microhardness of the Ni/Co - TiN nanocoating increased first and then decreased with the rising of the concentration of TiN nanoparticle, the jet speed of plating solution or the ultrasonic power. From the orthogonal experiment results, it could be obtained that the optimal process parameters were a jet speed of the plating solution of 4 m/s, an ultrasonic power of 120 W, and a concentration of TiN nanoparticle of 10 g/L. The Ni/Co grain sizes in the coating prepared using the optimal process parameters were obviously refined, TiN particles were dispersed in the coating, and the appearance of the coating was smooth and dense. Moreover, the microhardness of the coating was up to 689.82 HV, the friction coefficient was small, and the weight loss was small. The self - corrosion potential (Ecorr) and self - corrosion current density (Jcorr) were -0.338 V and 2.13×10-6 A/cm2, respectively.
