Electron-microscopy study of high-performance Nd-Fe-B permanent magnets prepared by rapid solidification route

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5529226

Chu, Tsungyao

Neodymium-iron-boron permanent magnets prepared by a rapid solidification route have been investigated in order to understand the process of crystallographic texture development that leads to a highly anisotropic structure and excellent permanent magnetic properties. The effects of alloying on the microstructure are also examined. Melt-spinning at optimal quench rate produces ribbons with a microstructure consisting of the Nd{sub 2}Fe{sub 14}B grains surrounded by a Nd-rich intergranular phase. Ribbons are slightly textured with the c-axes of the Nd{sub 2}Fe{sub 14}B grains tending to lie perpendicular to the ribbon surface, the texture being most pronounced near the free side of the ribbons. The intergranular phase has a fundamental fcc structure and a bcc superlattice with twice the dimension of the fcc cell. Interstitial atoms are believed to stabilize the Nd lattice in the fcc structure; some Nd sites are filled by dissolved Fe atoms. The interstitial atoms occupy specific sites, forming a superlattice having bcc symmetry. Finely dispersed Nd-rich precipitates exist in most of the large Nd{sub 2}Fe{sub 14}B grains; the precipitates obey a specific orientation relationship with their matrix grains. Ribbons are consolidated by hot-pressing; anisotropic grain growth leads to a microstructure of randomly oriented platelike Nd{sub 2}Fe{sub 14}B grains with each plate's wide, flat face normal to its c-axis. No noticeable difference in the microstructure results when small amounts of Co or Ga are added to the magnets; the alloying elements are incorporated indiscriminately into all the phases present and new compounds are not observed. With 15 wt.% of Co content, large grains of Nd(Fe,Co){sub 3}, a soft-magnetic phase with NdCo{sub 3}-type structure, form, leading to a decrease in coercivity.

• Research Organization: Texas Univ., Austin, TX (United States)
• OSTI ID: 5529226
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
360104 -- Metals & Alloys-- Physical Properties
ALLOYS
BORON ALLOYS
COBALT
CRYSTAL DEFECTS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
ELECTRON MICROSCOPY
ELEMENTS
FABRICATION
FCC LATTICES
GALLIUM
GRAIN GROWTH
HOT PRESSING
INTERSTITIALS
IRON ALLOYS
MAGNETIC PROPERTIES
MAGNETS
MATERIALS WORKING
METALLURGICAL EFFECTS
METALS
MICROSCOPY
MICROSTRUCTURE
NEODYMIUM ALLOYS
PERMANENT MAGNETS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POINT DEFECTS
PRESSING
RARE EARTH ALLOYS
SOLIDIFICATION
TRANSITION ELEMENTS
TWINNING