Corrosion characteristics of EB-PVD Ti/TiN multi-layer film coated Sm-Co and Fe-Nd-B magnets

To increase the corrosion resistance of magnetic materials, surfaces of Sm- Co and Nd-Fe-B based magnets were plated with Ti/TiN multi-layer and then e lectrochemical corrosion tests were performed in 4 kinds of electrolyte sol utions (0.9 vol%NaCl, 1 vol% lactic acid, 0.05 vol%HCl and modified Fusayam a's artificial saliva). Ti/TiN layer coated on magnet grows into preferred direction with lamellar structure and its thickness is 3.0 mum. Sm-Co base magnets coated with Ti/TiN multi-layer have good corrosion resistance in 1% lactic acid. Nd-Fe-B base magnets coated with Ti/TiN multi-layer showed go od tendency of corrosion resistance in 0.05 vol%HCl solution. The amount of elements released from both Sm-Co and Nd-Fe-B base magnets coated with Ti/ TiN multi-layer were more significantly decreased than that of uncoated one . The mean surface roughness values of both Sm-Co and Nd-Fe-B base magnets coated with Ti/TiN multi-layer were smaller than that of uncoated one after corrosion test. The decreasing rate of micro-hardness of both Sm-Co and Nd -Fe-B base magnets coated with Ti/TiN multi-layer were lower than that of u ncoated one after corrosion test. Magnets coated with Ti/TiN multi-layer pr oduced corrosion product such as TiO2 on the surface and resulted in better corrosion resistance than uncoated one.