Improved corrosion and temperature behaviour of modified Nd-Fe-B magnets

The characteristics of the high energy product NdFeB magnets obtained by the powder metallurgy route have been improved by appropriate vanadium additions. Specific combinations of V and Co lead to an intrinsic coercive force of about 1350 kA/m (17 kOe) in Dy-free magnets, without any large decrease of remanence. If 1.5-at.% Dy is added, load line down to -B/μH=0.5 can be achieved at 180°C without irreversible losses. Corrosion resistance is improved by blocking the selective oxidation of the Nd-rich phase. As a consequence, organic-coated magnets are able to withstand 15 days at 115°C-1.75 bars in a H₂O saturated atmosphere without any degradation. It is concluded that this set of new properties will enlarge the application fields of Nd-F-B permanent magnets