CRYSTAL AXIS ALIGNMENT IN HOT-DEFORMED SINTERED MAGNETS

We have investigated the possibility of hot deformation and crystallographic alignment in initially random (unaligned) sintered magnets which contain less Nd-rich phase and are characterized by better-defined grain boundaries than cast Pr-Fe-B-Cu, but contain more Nd-rich phase and larger grains than rapidly quenched and hot-pressed Nd-Fe-B (General Motors MQ-III). Nonaligned sintered magnets were found to deform at 1000-degrees-C under compressive stresses between 11 and 170 MPa. It was found that the addition of copper changed not only the melting point of the Nd-rich phase but also the surface energy of the liquid and its reaction with graphite. The crystal axis alignment is mainly attributed to the solution and reprecipitation of small grain fragments produced by deformation and by anisotropic crystal growth. A highly oriented structure was obtained in a sample of composition Nd15Fe77B6.5Cu1.5, after 24 h at 1000-degrees-C under a compressive stress of 45 MPa.