Structures and properties of sintered NdFeB coated with IBAD-Al/Al2O3 multilayers

IBAD-Al monolayers and amorphous Al2O3 monolayers were alternately deposited on sintered NdFeB magnets. IBAD-Al layers were prepared by direct current (DC) magnetron sputtering with ion-beam-assisted deposition (IBAD). Structure of the IBAD-Al/Al2O3 multilayers and their corresponding corrosion resistance and mechanical properties were investigated. Columnar structure is less visible in the IBAD-Al layers. Corrosion behaviour was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation and neutral salt spray (NSS) test. The IBAD-Al/Al2O3 bilayer and multilayers present very low corrosion current densities in potentiodynamic polarisation tests (~ 10− 11 A cm2). The top Al2O3 layers are critical to improve the corrosion resistance of Al based coatings. Furthermore, the hardness of multilayers is improved as the period decreases.