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.