Primary investigation of corrosion resistance of Ni-P/TiO2 composite film on sintered NdFeB permanent magnet

In this paper, an electroless nickel plating and sol–gel combined technique used to prepare the Ni-P/TiO2 composite film on sintered NdFeB permanent magnet is described and the composite film was characterized by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO2 film was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (icorr) of Ni-P/TiO2 composite film is 2.38μA/cm2 in 0.5mol/L H2SO4 solution about 33% of that of Ni-P coating and 0.22μA/cm2 in 0.5mol/L NaCl solution about 14% of that of Ni-P coating, respectively. In 0.5mol/L H2SO4 and 0.5mol/L NaCl solutions, the polarization resistance (Rp) of the composite film is 12.5kΩ cm2 and 120kΩ cm2, about 1.6 and 2 times that of Ni-P coating, respectively. The results indicate that Ni-P/TiO2 composite film has a better corrosion resistance than Ni-P coating.