Electroplating of anticorrosive Ni-TiO{sub}2 composite coatings on sintered NdFeB permanent magnets

摘要

Ni-TiO{sub}2 composite coatings were applied to sintered NdFeB permanent magnets by using a special pretreatment process and electrodeposition to increase corrosion resistance. Anatase (A) nano TiO{sub}2 particles and rutile (R) nano TiO{sub}2 particles were separately added to the Ni bath to fabricate the Ni-TiO{sub}2 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-TiO{sub}2 (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-TiO{sub}2(A) composite coating is compact and can effectively protect the NdFeB substrate from corrosion.