Recently, the grain boundary diffusion process (GBDP), involving heavy rare-earth elements such as Dy and Tb, has been widely used to enhance the coercivity of Nd-Fe-B permanent magnets. For example, a Dy compound is coated onto the surface of Nd-Fe-B sintered magnets, and then the magnets are heat treated. Subsequently, Dy diffuses into the grain boundaries of Nd-Fe-B magnets, forming Dy-Fe-B or Nd-Dy-Fe-B. The dip-coating process is also used widely instead of the GBDP. However, it is quite hard to control the thickness uniformity using dip coating. In this study, first, a DyF₃ paste is fabricated using DyF₃ powder. Subsequently, the fabricated DyF₃ paste is homogeneously coated onto the surface of a Nd-Fe-B sintered magnet. The magnet is then subjected to GBDP to enhance its coercivity. The weight ratio of binder and DyF₃ powder is controlled, and we find that the coercivity enhances with decreasing binder content. In addition, the maximum coercivity is obtained with the paste containing 70 wt% of DyF₃ powder.

A magnetic powder, M-type barium hexaferrite (BaFe12O19), was consolidated with the spark plasma sintering process. Three different holding temperatures, 850°C, 875°C and 900°C were applied to the spark plasma sintering process with the same holding times, heating rates and compaction pressure of 30 MPa. The relative density was measured simultaneously with spark plasma sintering and the convergent relative density after cooling was found to be proportional to the holding temperature. The full relative density was obtained at 900°C and the total sintering time was only 33.3 min, which was much less than the conventional furnace sintering method. The higher holding temperature also led to the higher saturation magnetic moment (σ_s) and the higher coercivity (H_c) in the vibrating sample magnetometer measurement. The saturation magnetic moment (σ_s) and the coercivity (H_c) obtained at 900°C were 56.3 emu/g and 541.5 Oe for each.

Citations

Citations to this article as recorded by  

• Effect of microwave sintering on density, microstructural and magnetic properties of pure strontium hexaferrite at low temperatures and heating rate
  Wail M. Matran, Mazli Mustapha, Mohd Faizairi Nor, Faizal Mustapha, Fahd Saeed Alakbari, Gamal Al-shawesh, Mohammed Bawahab
  Heliyon.2024; 10(20): e38766.     CrossRef
• A study of crystalline – texture and anisotropic properties of hexagonal BaFe12O19 sintered by in-situ magnetic-anisotropy spark plasma sintering (MASPS)
  Haetham G. Mohammed, Thar Mohammed Badri Albarody, Husam Kareem Mohsin Al-Jothery, Mazli Mustapha, N.M Sultan
  Journal of Magnetism and Magnetic Materials.2022; 553: 169268.     CrossRef
• Process Optimization of In Situ Magnetic-Anisotropy Spark Plasma Sintering of M-Type-Based Barium Hexaferrite BaFe12O19
  Haetham G. Mohammed, Thar Mohammed Badri Albarody, Susilawati Susilawati, Soheil Gohari, Aris Doyan, Saiful Prayogi, Muhammad Roil Bilad, Reza Alebrahim, Anwar Ameen Hezam Saeed
  Materials.2021; 14(10): 2650.     CrossRef
• Self-Consolidation and Surface Modification of Mechanical Alloyed Ti-25.0 at.% Al Powder Mixture by Using an Electro-Discharge Technique
  S.Y. Chang, H.S. Jang, Y.H. Yoon, Y.H. Kim, J.Y. Kim, Y.K. Lee, W.H. Lee
  Archives of Metallurgy and Materials.2017; 62(2): 1293.     CrossRef
• Plastic deformation and microstructural evolution during the shock consolidation of ultrafine copper powders
  Dong-Hyun Ahn, Wooyeol Kim, Minju Kang, Lee Ju Park, Sunghak Lee, Hyoung Seop Kim
  Materials Science and Engineering: A.2015; 625: 230.     CrossRef