Phase transformations and the development of magnetic coercivity in samarium-cobalt based permanent magnet alloys

Technical Report · Thu Sep 01 04:00:00 EDT 1983

OSTI ID:5274190

Rabenberg, L K

An experimental investigation of the microstructures of precipitation-hardening samarium-cobalt based magnets has been undertaken in order to determine the nature of the microstructural features critical for the development of high intrinsic coercivity in these permanent magnet alloys. In alloys aged near peak coercivity, three microstructural features are commonly observed. The bulk of the material consists of a modulated structure of twinned rhombohedral Sm/sub 2/(CoCuFeZr)/sub 17/ with thin layers of hexagonal Sm(CoCuFeZr)/sub 5/ developed on the six crystallographically equivalent pyramid planes. The modulated structure results from precipitation of 1:5 from supersaturated solution in 2:17; this precipitation reaction occurs concurrently with an allotropic transformation of the parent 2:17 phase. The thin plates nucleate at interfaces in the modulated structure and grow by a Zr diffusion limited dislocation mechanism. Aging these alloys at temperatures high enough for diffusion of Sm through the lattice results in coarsening of the modulations. In order to develop the coercivity, a low temperature aging process must be performed to allow Cu and Fe to partition into the Sm(CoCuFeZr)/sub 5/ and the Sm/sub 2/(CoCuFeZr)/sub 17/ phases, respectively. This increases the differences in their respective magnetic domain wall energies, increasing the barrier to domain wall propagation, resulting in higher intrinsic coercivity. Thus, the results of this investigation imply that high intrinsic coercivity in two-phase SmCo based permanent magnet alloys will occur if the microstructure consists of a continuous, coherent two-phase dispersion with maximal chemical differentiation between the two phases. 69 references, 58 figures, 6 tables.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5274190
• Report Number(s): LBL-16612; ON: DE84003045
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
COBALT ALLOYS
COBALT BASE ALLOYS
COERCIVE FORCE
CRYSTAL STRUCTURE
CRYSTALLOGRAPHY
DATA
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
INFORMATION
MAGNETS
MICROANALYSIS
MICROSCOPY
MICROSTRUCTURE
NUMERICAL DATA
PERMANENT MAGNETS
PHASE TRANSFORMATIONS
RARE EARTH ALLOYS
SAMARIUM ALLOYS
TRANSMISSION ELECTRON MICROSCOPY