Nd-Fe-B Nanoparticles through Surfactant Assisted Mechanical Milling and Alloy Design

Surfactant-assisted mechanical milling has been used to produce discrete nanoparticles of both Nd-Fe-B and Sm-Co amenable for bottom-up production of nanostructured or nanocomposite permanent magnets. However, in Nd-Fe-B the comminution of the material proceeds by transgranular fracture, which influences both the morphology of the nanoparticles and the magnetic properties. This paper utilizes alloy design to alter the fracture behavior from transgranular fracture to intergranular fracture. Nd-rich Nd2Fe14B alloys were produced by melt spinning in an overquenched state. The melt spun ribbons were annealed at 700°C and 800°C to ensure complete crystallization and to form different grain sizes. The resultant materials were then milled using a SPEX8000 mixer/mill with Oleic Acid as a surfactant for varying lengths of time. A second set of alloys was made with a 1 % S (atomic) addition, with the objective to embrittle the grain boundaries and force intergranular fracture. The coercivity decreased with increasing milling time for both S-less and S-containing alloys, from approximately 18 kOe to 3 kOe. The particle refinement process was also dependent on alloy composition, with the S-containing alloy showing a greater propensity for refinement. Adviser: Jeffrey E. Shiel