1. Acknowledgements – FAPESP, FAPERJ, CNPq, CAPES
Rietveld analysis of NdFeB as-cast samples
Suzilene R. Janasi1, Daniel Rodrigues2, Daniel L. Bayerlein3, Israel A. Cruz3, Marcos F. de Campos4
1IMAG Ind. Com. Ltda., Ribeirão Pires-SP, 2BRATS, Cajamar-SP, 3IPT, São Paulo-SP, 4UFF, Volta Redonda-RJ
Abstract
Several different phases can be found in NdFeB magnets. Usually the phi boride (Nd2Fe14B) is the most significant, and also the eta boride Nd1.1Fe4B4. Hexagonal Neodymium (Space Group =194) also can be found. However, impurity phases can also be present, as for example the alpha-iron phase (bcc). As the formation of Nd2Fe14B is the peritectic, slow cooling leads to formation of primary gamma iron (fcc), which subsequently transforms into alpha-iron, a deleterious phase for sintered magnets. Some intermetallic phases may also appear during solidification, as for example cubic NdFe2 (SG=227) or Nd3Fe (monoclinic SG=62, the same structure of cementite Fe3C). In order do find the best alloy composition, three as cast alloys with different nominal compositions were produced in a vacuum induction melting furnace with rapid cooling. Rietveld analysis were used to evaluate the amount of the magnetic phase (Nd2Fe14B) obtained as a function of the alloy composition.
AS CAST NdFeB ALLOYS
CONDITIONS OF THE ALLOYS PRODUCTION
Vacuum induction melting furnace;
Nd addition after FeB and Fe melting (Alloys 2 and 3);
Rapid cooling using a water cooled copper plate.
Alloy
Nominal Composition
Raw materials 1
Nd13Fe83B4
Commercial NdFeB alloy (LCM) 2
Nd15Fe77B8
Nd, FeB and 1006 carbon steel 3
Nd17Fe75B8
Nd, FeB and electrolytic Fe
ALLOY 1
Figure 2: Backscattering image and EDS spectra of the ALLOY 1 obtained in SEM-JEOL.
Figure 1: Optical microscopy of the ALLOY 1.
Figure 3: Rietveld analysis (TOPAS Academic 4.1) of the XRD spectra (Co ka o/min) of the ALLOY 1.
ALLOY 2
Figure 5: Backscattering image and EDS spectra of the ALLOY 2 obtained in SEM-JEOL.
Figure 4: Optical microscopy of the ALLOY 2.
Figure 6: Rietveld analysis (TOPAS Academic 4.1) of the XRD spectra (Co ka – 0.5 o/min) of the ALLOY 2.
ALLOY 3
Figure 8: Backscattering image and EDS spectra of the ALLOY 3 obtained in SEM-FEG.
Figure 7: Optical microscopy of THE ALLOY 3.
Figure 9: Rietveld analysis (TOPAS Academic 4.1) of the XRD spectra (Cu ka o/min) of the ALLOY 3.
Conclusions
Alloy 1, with low Nd content (29 wt%), presented a high Fe-a content (43%) and a low magnetic phase (phi boride, Nd2Fe14B) content. This will result in sintered magnets with low magnetic properties;
Alloys with high (Alloy 3, 36.5 wt%) or low (Alloy 1, 29 wt%) Nd content also present undesired phases as eta-boride (Nd1.1Fe4B4) and Fe-a.
Alloy 2 (33 wt% Nd) presented 99.8 % of the magnetic phase Nd2Fe14B, a desired condition to obtain sintered magnets with good magnetic properties.
Acknowledgements – FAPESP, FAPERJ, CNPq, CAPES