Clean Technology 2009

High-performance bulk nanostructured magnets

C.B. Rong and J.P. Liu
University of Texas at Arlington, US

Keywords: bulk nanocomposite magnets, energy product


Permanent magnetic materials have wide applications in daily life (such as in loudspeakers, motors and generators) and advanced technology (such as in aircrafts, space and weapon power systems). The so-called maximum energy product (BH)max is a measure of the energy stored in a magnet which is the figure of merit for permanent magnetic materials. The traditional permanent magnets are made of single phases. Unfortunately, (BH)max of single-phase magnets are limited by either low magnetization of hard magnetic phases or low magnetocrystalline anisotropy of soft phases. Advanced permanent magnets consist of hard and soft magnetic phases which are exchange-coupled in nanoscale and then provide high storage energy. However, it is still challenging to fabricate bulk nanocomposite materials for engineering applications without losing the nanoscale morphology of the magnets. In this work, we report on preparation and characterization of warm-compacted bulk nanocomposite magnets including FePt/Fe3Pt and SmCo5/-Fe. The chemically synthesized and ball-milled powders are compacted under the pressure of 2.5-4.0 GPa at different temperatures. The density can be reached to 90-99 % of theoretical density while the grain size is still very small (< 16nm) when the compacting temperature is < 600℃. The high density is considered to be due to the dropped yield strength and the effective lubrication mechanism in heated powders. Because of the fine microstructure and high density, high energy product about 16-17 MGOe can be obtained in the isotropic bulk nanocomposite magnets owing to the effective exchange coupling.
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