Performance of Nd-Fe-B Magnets Fabricated by Hot Isostatic Pressing and Low-Temperature Sintering
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JMEPEG (2019) 28:273–277 https://doi.org/10.1007/s11665-018-3832-6
Performance of Nd-Fe-B Magnets Fabricated by Hot Isostatic Pressing and Low-Temperature Sintering Fang Yang, Haiying Wang, Li You, Alex A. Volinsky
, Ce Zhang, Zhimeng Guo, and Yanli Sui
(Submitted April 12, 2018; in revised form September 17, 2018; published online December 17, 2018) Magnetic properties and microstructure of Nd-Fe-B sintered magnets fabricated by hot isostatic pressing (HIP) were studied. For comparison, magnets were also fabricated by vacuum sintering. The density reached 7.58 g/cm3 for the magnets HIP-sintered at 1123 K. The density of the magnets vacuum-sintered at 1123 K was much lower, which is of about 6.92 g/cm3. While the density of magnets vacuum-sintered at 1318 K was the same as the HIP-sintered magnets, the sintering temperature was significantly decreased to 1123 K. In addition, the average grain size decreased from 9 to 6 lm, which has enhanced coercivity. Therefore, the coercivity increased from 1067.7 to 1238.5 kA/m, which is 16% higher than the vacuumsintered magnets. HIP is a promising method to obtain high density and high coercivity Nd-Fe-B sintered magnets. Keywords
coercivity, grain refinement, hot isostatic pressing, NdFe-B sintered magnets
1. Introduction Due to excellent magnetic properties, Nd-Fe-B sintered magnets have attracted much attention in eco-friendly electrical applications, such as hybrid vehicles, electric vehicles, and wind power generators (Ref 1, 2). However, the relatively low coercivity cannot meet the growing requirements of elevated temperature operation (> 473 K) (Ref 3). To overcome this problem, heavy rare earth (HRE) elements, such as Dy or Tb, are commonly introduced into the Nd2Fe14B phase with a higher magnetic anisotropy field (Ref 4-6). Due to the scarcity and high cost, there is a strong demand to achieve high coercivity without using HRE elements. Among efforts to improve the coercivity of Nd-Fe-B sintered magnets without using HRE elements, one practical approach is to refine the grain size of the Nd2Fe14B phase (Ref 7, 8). Nd-Fe-B sintered magnetsÕ coercivity strongly depends on the grain size (Ref 9, 10). Hydrogen–disproportion–desorption recombination (HDDH) and jet milling (JM) applied in the powder making process can control commercial Nd-Fe-B powder size in the 3-5 lm range (Ref 11, 12). However, the grain growth is the most common problem found in sintering. It is well known that the addition of refractory metals, such as Mo, W, Nb, V, or Ta, can significantly suppress grain growth during sintering, due to the grain boundary pinning effect (Ref
Fang Yang, Haiying Wang, Ce Zhang, and Zhimeng Guo, Institute of Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China; Li You and Yanli Sui, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China; and Alex A. Volinsky, Department of Mechanical Engineering, University of South Florida, Tampa, FL 33620. Contact e-
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