Underwater explosive shock consolidation of nanocomposite Pr 2Fe14B/α-Fe magnetic powders

Abstract

Dynamic consolidation of powders was studied to fabricate exchange-coupled Pr2Fe14B/α-Fe nanocomposite bulk magnets, using explosively generated shock waves transmitted through water. The planar shock wave propagating into the powder had a peak pressure calculated to be ∼12GPa. Extensive plastic deformation of the powders and solid-state interfacial bonding of the ribbon flakes was obtained during shock compaction, resulting in fabrication of bulk compacts with nearly full density. Retention of nano-scale structure, and in fact further refinement of the grain size, ensured exchange coupling between the hard and soft phases, resulting in magnetic properties better than those of resin-bonded commercially available magnets. Post-shock annealing of the compacts at 750 and 850°C resulted in deterioration of the magnetic properties due to slight grain growth and decoupling of exchange interactions between hard and soft phases. The results illustrate that dynamic shock consolidation employing explosive loading is a viable method for fabricating bulk nanocomposite magnets and the rapid thermal excursions can be controlled to minimize and in fact eliminate the detrimental effects otherwise observed during high temperature sintering and annealing of the powders. © 2005 The Japan Institute of Metals.