Effect of Ni and Ni/Cr Coating on Corrosion and Magnetic Behavior of Sm₂Co₁₇ Substrate for Permanent Magnet Application in Marine Environment

In this study effect of Ni single-layer coating and Ni/Cr bilayer coating on room temperature corrosion of Sm₂Co₁₇ substrate in 3.5wt% NaCl solution was extensively performed. However, severe pitting corrosion occurred to the bare Sm₂Co₁₇ substrate and resulted in formation of cracks. Ni coating had good adhesion to the Sm₂Co₁₇ substrate but could not effectively improve the corrosion resistance of the substrate due to its porous nature. The Ni/Cr bilayer-coated magnet exhibited excellent corrosion resistance due to the prevention of Cl⁻ ions penetration by the Cr coating. Additionally, no prominent negative effect on magnetic properties was evidenced after Ni or Ni/Cr coating. Hence, based on above-mentioned outcome Ni/Cr coating above Sm₂Co₁₇ magnet is potentially recommended to mitigate the corrosion problem of permanent magnets operating in marine conditions.