Microstructural study of as-cast Nd-Fe-B alloys

The primary solidification or iron in Nd-Fe-B alloys is detrimental to the magnetic properties of sintered magnets; around the compositions of the ferromagnetic φ phase (Nd₂Fe₁₄ B) some fluctuations of the compositions and/or production processes control this solidification. A microstructural study of as-cast alloys by means of metallography, electron probe, and Mossbauer spectroscopy showed, besides the main φ phase, some amounts of α-Fe dendrites and intergranular precipitates of Nd_1.1Fe₄B₄ and of an Nd-rich phase. Following the observations, the boundary separating the primary crystallization field of Fe and φ can be more precisely defined. The optimal composition avoiding iron precipitation can be found