Effect of Cu in electroless Ni–Cu–P coating on passivation process

• Published in: Surface and interface analysis Vol. 49; no. 3; pp. 190 - 196
• Main Authors: Gan, Yiwei, Zhao, Tingting, Kang, Zhixin, Sang, Jing
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.03.2017
• Subjects: Chromium oxides; COATINGS; CORROSION; CORROSION PROTECTION; Corrosion resistance; Electroless coatings; electroless Ni–Cu–P coating; ELECTROLESS PLATING; formation mechanism; Interface analysis; Nickel; OXIDES; PASSIVATION; passive film; Protective coatings; X rays; XPS
• ISSN: 0142-2421; 1096-9918
• DOI: 10.1002/sia.6107

Electroless Ni–P and Ni–Cu–P coatings were passivated by chromate conversion treatment respectively. The anticorrosive performances of passivated coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The passivated Ni–Cu–P coating exhibited a high corrosion resistance with the icorr of 0.236 μA/cm,2 while the value of passivated Ni–P coating was only 1.030 μA/cm,2 indicating the passive film could improve the corrosion resistance of Ni–Cu–P coating to a significant extent. High‐resolution X‐ray photoelectron spectroscopy was used to determine the chemical states of elements detected in the passive film. Compared with passivated Ni–P coating, the passive film on Ni–Cu–P coating exhibited a higher ratio of Cr2O3 to Cr(OH)3 with the value of 72:28, which was the main factor for passivated Ni–Cu–P coating showing excellent corrosion resistance. The effect of Cu in electroless Ni–Cu–P coating on passivation process was discussed by the contrast experiment. Copyright © 2016 John Wiley & Sons, Ltd.