Bulk Nanocrystalline Nd-Fe-B Magnets Solidified in Magnetic Field With Various Surface Area-to-Volume Ratios

The bulk nanocrystalline Nd-Fe-B magnets in forms of rod and slab with various surface area-to-volume ratios (defined as S/V) were prepared by injection casting into copper molds. The effects of the surface area-to-volume ratio and the application of magnetic field during the casting process on the magnetic properties and microstructure of Nd_9.5Fe_71.5Ti_2.5Zr_0.5Cr₁B_14.5C_0.5 alloy have been studied. The results show that the samples that have larger S/V values exhibit higher _iH_c and (BH)_max. The intrinsic coercivity of bulk magnet is more sensitive to the cooling rate of alloy melt than the remanence. The slab-shaped sample cast with magnetic field has a stronger (00L) texture of Nd₂Fe₁₄B phase with the c-axis perpendicular to the slab plane than the slab-shaped sample cast without magnetic field. Applying a magnetic field during the casting process is helpful to refine the grain size, thus improving the magnetic properties.