PROPERTIES AND APPLICATIONS OF HIGH ... - Vacuumschmelze

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mass losses in mg/cm² Matrix Oxides Nd-rich constituents Nd-Fe-B Nd-Dy-Fe-TM-B Nd 2 Fe 14 B Nd 2 (Fe,Co) 14 B Nd 2O 3 Nd 2O 3 Nd Nd-(Co,Cu,Al) x VACODYM 6XX standard Nd-Fe-B exposition time in days Figure 10: Mass losses per surface area of sintered Nd-Fe-B magnets or Nd-Dy-Fe-Co-TM-B magnets with an improved corrosion resistance in dependence on the exposition time. Highly Accelerated Stress Test (HAST): 130 °C, 95 % relative humidity, 2.6 bar vapour pressure. The inset gives a model of the microstructure of standard sintered Nd-Fe-B magnets or new Nd-Dy-Fe- Co-TM-B magnets, respectively. The improved corrosion resistance is due to the replacement of the Nd-rich constituents by more noble Ndx(Co,TM)y compounds. Surface Thickness Method Colour Hardness Corrosion Temperature Resistance Range Sn >15 µm galvanic silver semibright HV 20 humid climate 10 µm galvanic silver semibright HV 350 humid climate 5 µm Ni + >10 µm Sn galvanic silver semibright HV 20 humid climate 5 µm spray- yellow 4 H excellent climatic, 5 µm IVD yellow 4 H excellent climatic, 15 µm EPP black 4 H excellent climatic, 6 µm EPP black 4 H excellent climatic,
5 Sintered Nd-Fe-B magnets with high energy densities and their applications The maximum energy density is determined by the remanent polarization and the reversible permeability µrev: ( BH ) J 2 max = r 4 ⋅ µ o ⋅ µ rev (1) In order to achieve a high maximum energy density the remanent polarization has to be optimized. The remanent polarization Jr is determined by: J ( ) ( ) ρ r 20° C = J S 20° C ⋅ ⋅ ( 1− V ) f ρ nonmag ⋅ 0. 01⋅ ϕ (2) ( ° C) 0 J s 20 , ρ ρ0 , Vnonmag and fφ denote the saturation polarization of the Nd2Fe14B compound at 20 °C, the density related to the theoretical density of the alloy, the fraction of nonmagnetic constituents and the alignment coefficient, respectively. The alignment coefficient is defined by: ⎛ ⎞ f ϕ = (cosϕ ⋅100%) with ⎜ J r⊥ ϕ = arctan 2 ⎟ ⎜ J ⎟ ⎝ r ⎠ (3) and represents the average misalignment angle φ of the grains with respect to the easy axis [14]. The precondition is a cylindrical symmetrical distribution of the misaligned grains. Magnets pressed isostatically or in an axial magnetic field meet this precondition fairly well. For magnets pressed in a transverse magnetic field the perpendicular components of the remanent polarization J r⊥ parallel or transverse to the pressing direction are different. Hence for transverse pressed magnets two alignment coefficients have to be distinguished. The alignment coefficients can be easily determined from the remanent polarization measured parallel J and perpendicular J with respect to the easy axis of an anisotropic magnet [14]. r r⊥ 5.1 Magnetic properties Optimized alloy-composition, proper alignment of the alloy-powders and controlled sintering and heat treatments result in isostatically pressed Nd-Fe-B blocks with a remanent polarization between 1.42 and 1.47 T, coercivities of about 9.5 kA/cm and maximum energy densities between 380 and 415 kJ/m³, see Fig. 3. Such magnets achieve alignment coefficients >96 %, what indicates an average misalignment angle of
Page 1 and 2: PROPERTIES AND APPLICATIONS OF HIGH
Page 3 and 4: max. energy density in kJ/m³ 450 4
Page 5 and 6: 2.3 Irreversible polarization losse
Page 7 and 8: 3.2 Special shapes for the reductio
Page 9: 4 Corrosion behaviour of sintered R
Page 13: tures between 50 and 150 °C. For a

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