Electrodeposition behavior and wear resistance of Co-Ni alloys from sulfamate baths for continuous steel casting mold

Electrodeposition behavior of Co-Ni alloys, which has been applied in the coating of continuous steel casting mold, was studied by measuring the polarization curves using a Cu substrate in sulfamate baths of various compositions at 55 °C under galvanostatic conditions. The wear resistance of electroplated Co-Ni film was also investigated by sliding wear test of ring-on-plate type at 300 °C. The results obtained were as follows: (1) In a wide range of bath composition, Co-Ni alloy deposition shows a feature of anomalous codeposition in which the less noble Co is electrodeposited in preference to Ni. The Ni deposition is greatly polarized when compared to the Co deposition from their single baths. Therefore, Co is deposited in preference to Ni, though Ni deposition from the alloy plating bath is more largely depolarized than that from its single bath. (2) The wear resistance of Co-Ni coating is improved with increasing Co content more than 50% in the deposits. The higher Co content in the deposit is, the thicker oxide film mainly composed of CoO and Co₃O₄ is formed on the surface of Co-Ni coating, which improves sliding property to prevent adhesive wear between Co-Ni coating and press ring.