Optimization of Liquid Dynamic Compaction for Fe-Nd-B Magnet Alloys
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OPTIMIZATICN CF LIQUID DYNAMIC CCXPACTICN FCR Fe-Nd-B MANET ALLOYS Mauri K. Veistinen*, Y. Hara, E.J. Lavernia , R.C. O'Handley and N.J. Grant Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambride, VA 02139 *Pernent address, Outokumpu Inc., Toolonkatu 4, P.O.Box 280, 00100 Helsinki, Finland ABSTRACT Permanent magnets from the Fe 7 7 Nd1 5 B8 alloy were produced using Process parameters such as gas and liquid dynamic compaction (LDC). metal mass flow rates were carefully controlled to refine the microstructure. Accordingly, grain sizes between 0.1 and 5 microns were achieved in the LDC compact. In contrast to our earlier LDC results high intrinsic coercivity in excess of 7500 Oe was obtained for thick (> 7 nm) as-LDC'd samples with lower neodymium content. INTRCDUCTION The liquid dynamic compaction (LDC) technique has been successfully used to produce isotropic permanent magnets of iron-neodymium-boron There are alloys directly from the melt in one processing step [1,2,3]. inherent advantages in the simplicity achieved by LDC processing (PM) powder metallurgy to conventional when compared particularly processes and melt-spinning which require several steps for magnet fabrication [4,5]. The LDC process can eliminate some of the steps such as fine-milling of master alloys, the handling of very reactive powders as well as the separate compacting and sintering stages. So far, however, the magnetic properties reported for Nd-Fe-B based permanent magnets produced by LDC have been less than optimum when compared to those materials produced by conventional PM processes as well as rapid solidification techniques such as melt spinning. This has been attributed in part to the isotropic microstructure of LDC magnets.
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addition, optimization of the processing parameters necessary for the spray deposition of Fe-Nd-B-magnets by LDC is yet to be completed. The best permanent magnetic properties recorded so tar for LDC materials have of the compact having a been for an Fe 76 NdlGBR alloy, in a section thickness of approximately 2 mmn[2]: Hci= 7 .5 kOe, B-7 kG, H_5 .5 kOe and (BH)ma 9-10 MGOe. However, when the thickness of the IDC compact was increaYsed from 2ram to 10 mm the intrinsic coercivity was found to be This substantial decrease in coercivity was attributed 30-40% lower [2]. to the relatively larger grain sizes associated with thicker sections of the deposit. Also, higher coercivity values were associated with high concentrations of neodymium in this earlier work [2]. For example, the intrinsic coercive force for alloys containing 18 a/o Nd was measured to be about 10 kOe while that for alloys with 14 a/o Nd was only about 3 kOe. Recently, isotropic Fe 7 LINdl.B permanent magnets have also been produced by plama spraying [6], which in principle, is a process similar to gas atomization. Intrinsic coercivities between 5 kOe and 11 kOe have been reported for the plasma-sprayed deposits. However, in these plasma-sprayed samples the average magnet thickness was under 0.5 mrm. In the
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