Microstructural and Electrochemical Characterization of Ni/Ti2N Composite Coating for Sintered NdFeB Permanent Magnets

Abstract

Sintered NdFeB magnets have complex microstructure that makes them susceptible to corrosion in humid or moist environments. The paper presents the anticorrosion characteristics of a novel Ni/Ti2N composite coating applied through electrodeposition and cathodic arc physical vapour deposition (CAPVD) to sintered NdFeB permanent magnets. The performance of composite coating was evaluated in simulated marine environment with the help of dc polarization techniques. The rate of coating degradation was also determined by employing ac electrochemical impedance spectroscopy (EIS). The coating morphology and surface chemistry were studied with scanning electron microscope (SEM). X-ray diffraction (XRD) was used for identification of component phases in the coating-substrate system. The results showed that the composite coating provided an adequately improved corrosion protection to the sintered NdFeB magnets in the simulated marine environment compared to the earlier reported ceramic and metallic coatings. The composite coating did not damage the magnetic properties of coating-substrate system that remained at par with the ceramic and nickel coating having copper interlayer.