Electroplating of anticorrosive Ni–TiO₂ composite coatings on sintered NdFeB permanent magnets

Abstract

Ni–TiO₂ composite coatings were applied to sintered NdFeB permanent magnets by using a special pretreatment process and electrodeposition to increase corrosion resistance. Anatase (A) nano TiO₂ particles and rutile (R) nano TiO₂ particles were separately added to the Ni bath to fabricate the Ni–TiO₂ composite coatings; for comparison, Ni-only coatings were also fabricated and assessed. X-ray diffraction and scanning electron microscopy were employed to examine the texture and the morphology of the coatings. Polarisation resistance tests show that the corrosion potential of Ni–TiO₂ (A) composite coating is about 600 mV higher than that of the NdFeB substrate in 3·5 wt-% NaCl solution, and as a result the corrosion current density drops. Both SEM and electrochemical impedance spectroscopy tests indicate that Ni–TiO₂ (A) composite coating is compact and can effectively protect the NdFeB substrate from corrosion.

Keywords:

• COMPOSITE ELECTRODEPOSITION
• NDFEB PERMANENT MAGNET
• NANO TIO2 PARTICLES
• CORROSION