Production of bulk amorphous and nanocomposite Nd4Fe77.5B18.5 materials by spark plasma sintering method

Amorphous melt-spun ribbons of an Nd₄Fe_77.5B_18.5 alloy were consolidated into bulk materials by a spark plasma sintering method. The resultant bulk materials were amorphous when the ribbons were consolidated at 773 K. The amorphous bulk materials showed a low coercivity as expected for amorphous Nd-Fe-B materials. Heat treatment of the bulk materials above the crystallization temperature resulted in the formation of a metastable Fe₃B phase together with an Nd₂Fe₁₄B phase. The resultant nanocomposite magnets showed a coercivity as high as 2.4 kOe as was the case for the annealed melt-spun ribbons. Such a bulk nanocomposite magnet with a high coercivity could be directly produced by the spark plasma sintering method. The bulk materials consolidated at 873 K consisted of Fe₃B and Nd₂Fe₁₄B phases and exhibited a high coercivity without heat treatment. The optimally annealed specimen showed a high remanence of 12 kG with the maximum energy product in excess of 10 MGOe.