Study on The Corrosion Behavior of NdFeB Permanent Magnets in NaCl Solutions with PVD Techniques

The corrosion resistance of NdFeB magnets is improved by direct NiCrAlV and NiCrAlVN thin film treatment of a sintered NdFeB magnet surface. X-ray diffraction and transmission electron microscopy are used to examine the microstructure of the thin films. The hardness, wettability, and surface roughness of the thin films are investigated using nanoindentation, contact angle measurements, and atomic force microscopy, respectively. The NiCrAlV and NiCrAlVN thin films exhibit a typical amorphous microstructure and a smooth surface with an average roughness of about 2 nm. The results of alternating-current (ac) impedance spectroscopy in 5% NaCl solution show that the ac impedance of the thin films increased with time. The |Z |10 mHz values for NiCrAlVN ( 15\thinspace000 ohms/cm
²
), NiCrAlV ( 4000 ohms/cm
²
), and uncoated NdFeB magnets ( 550 ohms/cm
²
) show an eight-fold increase in the low-frequency impedance due to the amorphous state.