An alternative fabrication method for carburizing steel using spark plasma sintering (SPS) is investigated. The sintered carburized sample, which exhibits surface modification effects such as carburizing, sintered Fe, and sintered Fe–0.8 wt.%C alloys, is fabricated using SPS. X-ray diffraction and micro Vickers tests are employed to confirm the phase and properties. Finite element analysis is performed to evaluate the change in hardness and analyze the carbon content and residual stress of the carburized sample. The change in the hardness of the carburized sample has the same tendency to predict hardness. The difference in hardness between the carburized sample and the predicted value is also discussed. The carburized sample exhibits a compressive residual stress at the surface. These results indicate that the carburized sample experiences a surface modification effect without carburization. Field emission scanning electron microscopy is employed to verify the change in phase. A novel fabrication method for altering the carburization is successfully proposed. We expect this fabrication method to solve the problems associated with carburization.

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.

We investigate the microstructural and magnetic property changes of DyH₂, Cu + DyH₂, and Al + DyH₂ diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusiontreated magnets increases with increasing heat treatment temperature except at 910°C, where it decreases slightly. Moreover, at 880°C, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed DyH₂-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only DyH₂. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of 790-880°C. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed DyH₂, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic (Nd, Dy)₂Fe₁₄B phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

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• Synthesize of Nd₂Fe₁₄B Powders from 1-D Nd₂Fe₁₄B Wires using Electrospinning Process
  Nu Si A Eom, Su Noh, Muhammad Aneeq Haq, Bum Sung Kim
  Journal of Korean Powder Metallurgy Institute.2019; 26(6): 477.     CrossRef

In this study, we investigate the effect of the diffusion barrier and substrate temperature on the length of carbon nanotubes. For synthesizing vertically aligned carbon nanotubes, thermal chemical vapor deposition is used and a substrate with a catalytic layer and a buffer layer is prepared using an e-beam evaporator. The length of the carbon nanotubes synthesized on the catalytic layer/diffusion barrier on the silicon substrate is longer than that without a diffusion barrier because the diffusion barrier prevents generation of silicon carbide from the diffusion of carbon atoms into the silicon substrate. The deposition temperature of the catalyst and alumina are varied from room temperature to 150°C, 200°C, and 250°C. On increasing the substrate temperature on depositing the buffer layer on the silicon substrate, shorter carbon nanotubes are obtained owing to the increased bonding force between the buffer layer and silicon substrate. The reason why different lengths of carbon nanotubes are obtained is that the higher bonding force between the buffer layer and the substrate layer prevents uniformity of catalytic islands for synthesizing carbon nanotubes.

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• A Study on Residual Powder Removing Technique of Multi-Layered Graphene Based on Graphene One-Step Transfer Process
  Chae-young Woo, Yeongsu Jo, Soon-kyu Hong, Hyung Woo Lee
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 11.     CrossRef
• Fabrication of robust, ultrathin and light weight, hydrophilic, PVDF-CNT membrane composite for salt rejection
  Vivek Dhand, Soon Kyu Hong, Luhe Li, Jong-Man Kim, Soo Hyung Kim, Kyong Yop Rhee, Hyung Woo Lee
  Composites Part B: Engineering.2019; 160: 632.     CrossRef

The en-riched ⁵⁸Ni powders are dissolved in acid solution and coated on a Cu target for proton irradiation at cyclotron to produce ⁵⁷Co radioisotope. The condition of the plating bath and the coating process are determined using the en-riched powders. To establish the coating conditions for ⁵⁷Co, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a rhodium plate. The thermal diffusion of electroplated Co into a rhodium matrix was studied to apply a ⁵⁷Co Mssbauer source. The diffusion depth from surface to matrix of Co is depended on the annealing temperature and time. The deposited Co atoms diffuse completely into a rhodium (Rh) matrix without substantial loss at an annealing temperature of 1200 for 4 hours.