Jong Min Byun

Grain refinement in heavy rare earth element-free sintered Nd–Fe–B magnets by addition of a small amount of molybdenum

We employed a modified refractory-metal-addition method to achieve higher coercivity and remanence in heavy rare earth element (HREE)-free Nd–Fe–B sintered magnets. This process involved inducing the formation of a homogeneous secondary phase at the grain boundaries during sintering, making it possible to control the intergrain diffusion by adding small amounts of Mo, a refractory metal. To control the microstructure of the secondary phase effectively, a metal organic compound of the refractory metal was coated on the surfaces of the particles of an HREE-free Nd–Fe–B powder. The average grain size after this process was 5.60 μm, which was approximately 1.8 μm smaller than that of the HREE-free sintered Nd–Fe–B magnets (7.4 μm). The coercivity of the magnets prepared through this process could be increased from 11.88 kOe to 13.91 kOe without decreasing their remanence.

Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo5SiB2 and Mo3Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.

Synthesis of CNT on a Camphene Impregnated Titanium Porous Body by Thermal Chemical Vapor Deposition

【In this study, titanium(Ti) meshes and porous bodies are employed to synthesize carbon nanotubes(CNTs) using methane(

CNT Growth Behavior on Ti Substrate by Catalytic CVD Process with Temperature Gradient in Tube Furnace

CH_4

Evaluation of the Mechanical Properties of Zn-Mg Alloys with Composition of Mg

) gas and camphene solution, respectively, by chemical vapor deposition. Camphene is impregnated into Ti porous bodies prior to heating in a furnace. Various microscopic and spectroscopic techniques are utilized to analyze CNTs. It is found that CNTs are more densely and homogeneously populated on the camphene impregnated Ti-porous bodies as compared to CNTs synthesized with methane on Ti-porous bodies. It is elucidated that, when synthesized with methane, few CNTs are formed inside of Ti porous bodies due to methane supply limited by internal structures of Ti porous bodies. Ti-meshes and porous bodies are found to be multi-walled with high degree of structural disorders. These CNTs are expected to be utilized as catalyst supports in catalytic filters and purification systems.】

Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles

In this study, modified catalytic chemical vapor deposition (CCVD) method was applied to control the CNTs (carbon nanotubes) growth. Since titanium (Ti) substrate and iron (Fe) catalysts react one another and form a new phase (Fe2TiO5) above 700 C, the decrease of CNT yield above 800C where methane gas decomposes is inevitable under common CCVD method. Therefore, we synthesized CNTs on the Ti substrate by dividing the tube furnace into two sections (left and right) and heating them to different temperatures each. The reactant gas flew through from the end of the right tube furnace while the Ti substrate was placed in the center of the left tube furnace. When the CNT growth temperature was set 700/950C (left/right), CNTs with high yield were observed. Also, by examining the microstructure of CNTs of 700/950C, it was confirmed that CNTs show the bamboo-like structure.

저온 브레이징용 Al-Si-Cu 합금의 Sn 첨가에 따른 융점 및 기계적 특성 변화 연구

In this study, Zn-Mg alloys with various Mg contents were manufactured by the casting method using an induction melting furnace. Then microstructure analysis and mechanical property tests were carried out. In the Zn-Mg alloy with a content of less than 7 wt%Mg, the hardness of the Zn-Mg alloys gradually increased as the Mg content increased but in the alloy with more than Zn-7 wt%Mg, the hardness was almost the same. Enhanced hardness is induced by the intermetallic compounds phase of Mg2Zn11 and MgZn2. In the compression test, Zn-3 wt%Mg had the best compression strength at 610 MPa, but Zn-7 wt%Mg and Zn-10 wt%Mg had a low compression strength at 343 Mpa and 111 MPa, respectively, although these alloys have excellent hardness. This study verified that Zn-Mg alloys containing a Zn phase have more toughness than those composed of only intermetallic compounds such as Mg2Zn11 and MgZn2. (Received November 19, 2012)

Fabrication of Ti Porous body with Improved Specific Surface Area by Synthesis of CNTs

In recent years, refractory materials with excellent high-temperature properties have been in the spotlight as a next generation’s high-temperature materials. Among these, Mo-Si-B alloys composed of two intermetallic compound phases (Mo5SiB2 and Mo3Si) and a ductile α-Mo phase have shown an outstanding thermal properties. However, due to the brittleness of the intermetallic compound phases, Mo-Si-B alloys were restricted to apply for the structural materials. So, to enhance the mechanical properties of Mo-Si-B alloys, many efforts to add rare-earth oxide particles in the Mo-Si-B alloy were performed to induce the improvement of strength and fracture toughness. In this study, to investigate the effect of adding nano-sized Y2O3 particles in Mo-Si-B alloy, a core-shell powder consisting of intermetallic compound phases as the core and nano-sized α-Mo and Y2O3 particles surrounding the core was fabricated. Then pressureless sintering was carried out at 1400 °C for 3 h, and the mechanical properties of sintered bodies with different amounts of Y2O3 particles were evaluated by Vickers hardness and 3-point bending test. Vickers hardness was improved by dispersed Y2O3 particles in the Mo-Si-B alloy. Especially, Mo-3Si-1B-1.5Y2O3 alloy had the highest value, 589 Hv. The fracture toughness was measured using Mo-3Si-1B-1.5Y2O3 alloy and the value indicated as 13.5 MPa·√m.

Research Trend of Additive Manufacturing Technology − A=B+C+D+E, add Innovative Concept to Current Additive Manufacturing Technology: Four Conceptual Factors for Building Additive Manufacturing Technology −

This work was supported by the Technological Innovation R&D Program(S2161336) funded by the Small and Medium Business Administration(SMBA, Korea). This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (2016-R1A6A1A03013422).

A Phenomenological Analysis on the Anisotropic Shrinkage of Nd–Fe–B Compacts During Sintering Process

This study is performed to fabricate a Ti porous body by freeze drying process using titanium hydride () powder and camphene. Then, the Ti porous body is employed to synthesize carbon nanotubes (CNTs) using thermal catalytic chemical vapor deposition (CCVD) with Fe catalyst and methane () gas to increase the specific surface area. The synthesized Ti porous body has -sized macropores and -sized micropores. The synthesized CNTs have random directions and are entangled with adjacent CNTs. The CNTs have a bamboo-like structure, and their average diameter is about 50 nm. The Fe nano-particles observed at the tip of the CNTs indicate that the tip growth model is applicable. The specific surface area of the CNT-coated Ti porous body is about 20 times larger than that of the raw Ti porous body. These CNT-coated Ti porous bodies are expected to be used as filters or catalyst supports.