| Piston ring is a key accessory of marine diesel engine and automobile engine. It's required excellent thermal stability, wear resistance and corrosion resistance for being in high temperature, high pressure, alternating mechanical loads working condition. How to prolong its service life is always a research hotspot for scholars in materials science. In this paper, amorphous Cr-C alloy coating was prepared by electrodepo siting, its preparation process and properties were discussed.Amorphous Cr-C alloy coatings were prepared in hexavalent and trivalent chromium baths respectively. Explored principally how to tartaric acid additives, current density, pH value and depositional time influence Coating structure, hardness and thickness. The results showed that the hexavalent chromium bath could produce amorphous Cr-C alloy coating owning perfect structure and hardness when tartaric acid concentration was 40g/L, current density for 20～30A/dm2, pH=2.0. The coating owned compact structure without crack, hardness of 997HV and Carbon of 2.67wt%, whose thickness could reach 16 microns once, even more than 20 microns deposited repeatedly after burnished. The trivalent chromium bath containing CrCl3·6H2O also produced amorphous Cr-C alloy coating that had hardness of 875.6HV and thickness of 7 microns around. It couldn't be deposited repeatedly to increase its thickness and the test results couldn't reproduce faultlessly because of poor stability of the plating solution.Compared with conventional crystalline state Cr coating, amorphous Cr-C alloy coating owned preferable properties. Scratches experimental results showed that the critical load of amorphous Cr-C coating was more than that of conventional coating and only a little coating had stripped. It indicated amorphous Cr-C coating had better adhesion. Wear test results showed that, in same conditions, Friction coefficient and wear weight loss of amorphous Cr-C coating were both far less than that of conventional coating. It indicated amorphous Cr-C coating had more excellent wearability, which result from the high hardness and atoms non-directional movement. Electrochemical polarization curve showed that corrosion potential of amorphous Cr-C coating in lmol/L H2SO4 and NaCl solution both shifted to the right compared with conventional crystalline state Cr coating, and the electrochemical impedance spectroscopy arc increased. It revealed amorphous Cr-C coating owned better corrosion resistance because of its uniform structure and composition which leaded to inhibit the electrochemical corrosion points.Amorphous Cr coating began to crystal transition with the rising temperature. In the crystallization process, the hardness of the coating increased due to microcrystalline strengthening and dispersion strengthening of the precipitation Cr7C3 and Cr23C6. It reached the maximum 1610HV at 600℃around. But, when the temperature was higher than 600℃, the coarsening of Cr crystalline grains and the growth of the interstitial phase caused the rapid decrease of the hardness.
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