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Multistep Heat-Treatment Effects on Electrospun Nd-Fe-B-O Nanofibers

Jeon E. J., Eom N. S. A., Lee J., Lee B., Cho H. M., On J. S., Choa Y.-H, Kim B. S.

Archives of Metallurgy and Materials

2018

Vol. 63, iss. 3

1433--1437

Neodymium-Iron-Boron (Nd-Fe-B) magnets are considered to have the highest energy density, and their applications include electric motors, generators, hard disc drives, and MRI. It is well known that a fiber structure with a high aspect ratio and the large specific surface area has the potential to overcome the limitations, such as inhomogeneous structures and the difficulty in alignment of easy axis, associated with such magnets obtained by conventional methods. I n this work, a suitable heat-treatment procedure based on single-step and multistep treatments to synthesize sound electrospun Nd-Fe-B-O nanofibers of Φ572 nm was investigated. The single-step heat-treated (directly heat-treated at 800°C for 2 h in air) samples disintegrated along with the residual organic compounds, whereas the multistep heat-treated (sequential three-step heat-treated including three steps;: dehydration (250°C for 30 min in an inert atmosphere), debinding (650°C for 30 min in air), and calcination (800°C for 1 h in air)) fibers maintained sound fibrous morphology without any organic impurities. They could maintain such fibrous morphologies during the dehydration and debinding steps because of the relatively low internal pressures of water vapor and polymer, respectively. In addition, the NdFeO3 alloying phase was dominant in the multistep heat-treated fibers due to the removal of barriers to mass transfer in the interparticles.

Fabrication and Characterization of CoCrFeNiMn High Entropy Alloy Powder Processed by Gas Atomization

Park T. G., Lee S. H., Lee B., Cho H. M., Choi W. J., Kim B. S., Shin K. S., Kim T.-S.

Archives of Metallurgy and Materials

2018

Vol. 63, iss. 2

1055--1059

In this study, precisely controlled large scale gas atomization process was applied to produce spherical and uniform shaped high entropy alloy powder. The gas atomization process was carried out to fabricate CoCrFeNiMn alloy, which was studied for high ductility and mechanical properties at low temperatures. It was confirmed that the mass scale, single phase, equiatomic, and high purity spherical high entropy alloy powder was produced by gas atomization process. The powder was sintered by spark plasma sintering process with various sintering conditions, and mechanical properties were characterized. Through this research, we have developed a mass production process of high quality and spherical high entropy alloy powder, and it is expected to expand applications of this high entropy alloy into fields such as powder injection molding and 3D printing for complex shaped components.

Thermal Aging of Unsaturated Polyester Composite Reinforced with E-Glass Nonwoven Mat

Hossain M., Elahi A. H. M. F., Afrin S., Mahmud I., Cho H. M., Khan M. A.

Autex Research Journal

2017

Vol. 17, no. 4

313--318

An experiment was carried out using glass fiber (GF) as reinforcing materials with unsaturated polyester matrix to fabricate composite by hand layup technique. Four layers of GF were impregnated by polyester resin and pressed under a load of 5 kg for 20 hours. The prepared composite samples were treated by prolonged exposure to heat for 1 hour at 60-150°C and compared with untreated GF-polyester composite. Different mechanical test of the fabricated composite were investigated. The experiment depicted significant improvement in the mechanical properties of the fabricated composite resulted from the heat treatment. The maximum tensile strength of 200.6 MPa is found for 90°C heat-treated sample. The mechanical properties of the composite do seem to be very affected negatively above 100°C. Water uptake of the composite was carried out and thermal stability of the composite was investigated by thermogravimetric analysis, and it was found that the composite is stable up to 600°C. Fourier transform infrared spectroscopy shows the characteristic bond in the composite. Finally, the excellent elevated heat resistant capacity of glass-fiber-reinforced polymeric composite shows the suitability of its application to heat exposure areas such as kitchen furniture materials, marine, and electric board.