Nanocrystalline Co Ni alloy coatings were prepared by direct current(DC),unipolar and bipolar pulse electrodeposition techniques.The surface morphology and surface roughness of the coatings were characterized with atomic force microscope(AFM)and a surface profile measurement system.The microhardness was measured on a MV 2T Vickers microhardness tester.The friction and wear properties of the coatings wear evaluated using a ball on disc tribometer and their worn surfaces were studied by SEM to illustrate their wear mechanisms.The results show that the morphology,hardness and the tribological properties of the nanocrystalline Co Ni coatings are significantly affected by the electrodeposition techniques.DC electrodeposition results in the as prepared Co Ni coating having low surface roughness,low hardness,and the columnar crystal with big size.The Co Ni coating produced by the bipolar pulse electrodeposition exhibits the highest hardness,the smallest surface roughness,and the columnar crystals with the smallest size.The wear resistance of the Co Ni coating produced by the bipolar pulse electrodeposition is improved almost one order of magnitude when compared to the Co Ni coating produced by DC eletrodeposition.The coating produced by DC eletrodeposition exhibits the severely adhesive and abrasive wear during the sliding process.However the coating produced by bipolar pulse eletrodeposition exhibits the slightly fatigue and abrasive wear.