Novel Ni/Ti 2 N composite coating for sintered NdFeB permanent magnets

Abstract

The paper presents the anticorrosion characteristics of a novel Ni/Ti₂N composite coating applied through electrodeposition and cathodic arc physical vapour deposition for protection of sintered NdFeB permanent magnets that are susceptible to corrosion in active environments. The composite coating was evaluated in simulated marine and industrial environments with the help of dc polarisation techniques. The rate of coating degradation was determined through ac electrochemical impedance spectroscopy. The coating morphology and surface chemistry were studied with scanning electron microscope. X‐ray diffraction was used for the identification of component phases in the coating–substrate system. The results showed that the corrosion current density i_Corr of the composite coated NdFeB magnets came out to be 0·8575 and 0·3011 μA cm⁻² that is about 10 and 4% of the ceramic coated NdFeB magnets in the marine and industrial environments respectively. The magnetic properties remained unaffected and were as good as for the uncoated, NiCuNi and ceramic coated NdFeB magnets.