Solidification process in melt spun Nd-Fe-B type magnets
- Iowa State Univ., Ames, IA (United States)
A generalized solidification model has been developed based on a systematic investigation on the microstructure of melt spun Nd-Fe-B alloys. Melt spinning was conducted on initial stoichiometric and TiC added Nd2Fe14B (2-14-1) compositions to produce under, optimally and over quenched microstructures. Microstructural characterization was carried out by TEM, SEM, Optical microscopy, XRD, DTA, VSM and DC SQUID techniques. By taking the dendritic breakup during recalescence into consideration, this generalized model has successfully explained the solidification process of the melt spun Nd-Fe-B alloys. Challenging the conventional homogeneous nucleation models, the new model explains the fine and uniform equiaxed 2-14-1 microstructure in optimally quenched ribbons as a result of the breakup of the 2-14-1 dendrites which nucleate heterogeneously from the wheel surface and grow dendritically across the ribbon thickness due to the recalescence. Besides this dendritic breakup feature, the under quenched microstructure is further featured with another growth front starting with the primary solidification of Fe phase near the free side, which results in a coarsely grained microstructure with Fe dendritic inclusions and overall variation in microstructure across the ribbon thickness. In addition, because a epitaxy exists between the Fe phase and the 2-14-1, the so-formed coarse 2-14-1 grains may be textured. C-axis texturing was observed in under quenched ribbons. As a constraint to solidification models in this system, the cause and characteristics of this phenomenon has been studied in detail to test the authors proposed model, and agreement has been found. An extension has also been made to understand the solidification process when TiC is added, which suggests that Ti and C slow down the growth front of both Fe and 2-14-1 phase.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 654150
- Report Number(s):
- IS-T-1833; ON: DE98004653; TRN: AHC2DT05%%239
- Resource Relation:
- Other Information: DN: Thesis submitted to Iowa State Univ., Ames, IA (US); TH: Thesis (M.S.); PBD: 23 Feb 1998
- Country of Publication:
- United States
- Language:
- English
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