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

• Published in: Journal of applied physics 1991-11, Vol.70 (10), p.6375-6375
• Main Authors: Lin, K. D., Tzuoo, U. C., Tung, J. Y., Chin, T. S.
• Format: Article
• Language: English
• Subjects: 360104 - Metals & Alloys- Physical Properties; ALLOYS; ANNEALING; BORON ALLOYS; COBALT ALLOYS; COERCIVE FORCE; CRYSTAL STRUCTURE; DYSPROSIUM ALLOYS; FABRICATION; GRAIN BOUNDARIES; HEAT TREATMENTS; IRON ALLOYS; MATERIALS; MATERIALS SCIENCE; MICROSTRUCTURE; NEODYMIUM ALLOYS; RARE EARTH ALLOYS; REACTIVITY COEFFICIENTS; SINTERED MATERIALS; SINTERING; TEMPERATURE COEFFICIENT
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.349947

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.