Effect of producation method on the microstructure and corrosion properties of ndfeb alloy

Melt spun Nd (30%wt)- Fe(69%wt)- B(1wt%) magnetic alloy was prepared in the ribbon and powder forms. The alloy in both forms was investigated by using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy associated with SEM (SEM-EDS) and X-ray diffraction techniques. The corrosion performance of both forms of the alloy was evaluated using Tafel Polarization and electrochemical impedance (EIS) techniques which were carried out using Gamry potentiostat. Surface investigations revealed the presence of Fe, Nd-Fe-B, Nd and B phases. Elemental distribution mapping performed using the SEM instrument for the powder and ribbon reveal relatively large regions for Nd only; small regions for B only; regions for Fe only and large region for NdFeB where the percent for elements are (1%, 3%, 96%) for B,Nd and Fe, respectively. These results substantiated by the results of are EDS analysis Corrosion investigation revealed that the alloy in the powder form show very low corrosion current and corrosion rate in comparison to the melt-spun alloy. In normal water corrosion current and corrosion rate obtained for the alloy in the powder form are about 4 times lower than those obtained for the melt spun alloy. In sea water environment, corrosion current and corrosion rate are 160 times lower for the alloy in the powder form. The poor corrosion resistance of the melt-spun alloy in sea water environment is due to the highly reactive rare earth element upon which the alloys are based (Nd) as well as an electrochemical coupling between phases present in the bulk alloy. Key Words: Rapid solidification, microstructure, NdFeb alloys, corrosion