Effect of Pulsed Plasma Treatment on Structure and Corrosion Behavior of Sm-Co and Nd-Fe-B Magnets

The combination of conventional ion-plasma deposition and pulsed plasma technologies (PPT) has been applied for rare-earth Sm-Co and Nd-Fe-B based magnets, to provide them with enhanced corrosion resistance. The influence of pulsed plasma treatment on Sm-Co magnets with deposited titanium coatings has been investigated. It was revealed that the thickness of modified layer significantly depends on the thickness of initial titanium film and plasma treatment regimes. As a result of plasma treatment with energy density of 30 J/cmb for 5 pulses fine-grained layer with me thickness of 70 microns has been formed on the Sm-Co magnet with pure titanium film of 50 μm. According to SEM analyses considerable diffusion of titanium to the bulk of the magnet on the depth of 20 microns took place. Such reaction enhances strong bonding between the coating and the magnet. The effects of plasma processing on corrosion properties of Nd-Fe-B sintered magnets with ferroboron Fe80B20 (wt.%) coatings have been studied. The tests were carried out in naturally aerated sodium sulphate solutions by polarization method. It was shown that polishing of the initial surface before plasma treatment and ferroboron deposition have a strong influence on the corrosion behavior of Nd-Fe-B magnets.