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Effect of refractory additives on coercivity of sintered (Nd, Dy)(Fe, Co) BM magnets (M=Cr/W/Zr/Nb/Ta) (abstract)

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4 Author(s)
Lin, K.D. ; High‐End Metals Corporation, Hsinchu Industrial Park, Hukou, 303, Taiwan, Republic of China ; Tzuoo, U.C. ; Tung, J.Y. ; Chin, T.S.

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In a trial to develop heat‐resistant sintered Nd2Fe14B magnets, a refractory element (Cr/W/Zr/Nb/Ta) was selected as an additive incorporating Dy and Co in the Nd‐Fe‐B composition. Nd13Dy1.5Fe72-xCo6B7.5Mx alloys (M=Cr/W/Nb/Ta, x=0, or 3.5) were arc‐melted, pulverized, compacted, and sintered by the conventional powder metallurgy method. It was found that W/Cr greatly enhances the as‐sintered intrinsic coercivity (iHc, in kA/m), e.g., from 510 (x=0) to 810 (W, x=3.5) or 740 (Cr, x=3.5). An additional two‐stage annealing at 900 and 600 °C for 1 h each led to an even higher iHc of 1000 (W, x=3.5). While Nb/Ta moderately enhanced as‐sintered iHc, and responded less to additional annealing. Temperature coefficients of remanence was found to be greatly improved by the W or Cr addition, e.g., 0.43%/°C for x=0 and 0.06%/°C for M=W, x=3.5 (p=1, 20–150 °C). They are thus very suitable for applications at temperatures up to 150 °C. EPMA analyses showed the possible existence of a M2FeB2 (M=W/Nb/Ta) phase at grain boundaries. Thermomagnetic analyses and detailed microstructure of the sintered and/or annealed magnets are discussed.

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Journal of Applied Physics  (Volume:70 ,  Issue: 10 )