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방전플라즈마 소결법으로 제작된 순 마그네슘 분말 소결체의 특성평가
홍지민,손현택,장세훈,이재설,차용훈,오익현,Hong, Ji-Min,Son, Hyeon-Taek,Chang, Se-Hun,Lee, Jae-Seoul,Cha, Yong-Hun,Oh, Ik-Hyun 한국재료학회 2007 한국재료학회지 Vol.17 No.6
The pure Mg powder compacts were successfully fabricated using SPS process. The machined chip powder showed flake shaped morphology with coarse surfaces, while gas atomized powders were spherical in morphology with smooth surfaces. In this study, SPS process was used to consolidate the pure Mg powder because this process allows high density consolidation in a short time. The results showed that increased sintering temperature from $350^{\circ}C$ to $500^{\circ}C$ with pressure of 30MPa, the maximum values of the density was increased from 98.1% to 99.8% of theoretical density, respectively. However, density of the sintered chip powders was higher than that of gas-atomized powder due to larger contact areas between particles.
송국현,손현택,김대근,김한솔,김원용,Song, Kuk-Hyun,Son, Hyun-Taek,Kim, Dae-Keun,Kim, Han-Sol,Kim, Won-Yong 한국재료학회 2011 한국재료학회지 Vol.21 No.5
The present study was carried out to evaluate the microstructural and mechanical properties of cross-roll rolled pure copper sheets, and the results were compared with those obtained for conventionally rolled sheets. For this work, pure copper (99.99 mass%) sheets with thickness of 5 mm were prepared as the starting material. The sheets were cold rolled to 90% thickness reduction and subsequently annealed at $400^{\circ}C$ for 30 min. Also, to analyze the grain boundary character distributions (GBCDs) on the materials, the electron back-scattered diffraction (EBSD) technique was introduced. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets with an average size of 100 ${\mu}M$. In particular, the average grain size became smaller by cross-roll rolling (6.5 ${\mu}M$) than by conventional rolling (9.8 ${\mu}M$). These grain refinements directly led to enhanced mechanical properties such as Vickers micro-hardness and tensile strength, and thus the values showed greater increases upon cross-roll rolling process than after conventional rolling. Furthermore, the texture development of <112>//ND in the cross-roll rolling processed material provided greater enhancement of mechanical properties relative to the case of the conventional rolling processed material. In the present study, we systematically discuss the enhancement of mechanical properties in terms of grain refinement and texture distribution developed by the different rolling processes.
방전플라즈마 소결공법을 이용한 Mg<sub>97</sub>Y<sub>2</sub>Zn<sub>1</sub> 합금 소결체의 특성평가
홍지민,손현택,장세훈,이재설,차용훈,오익현,Hong, Ji-Min,Son, Hyeon-Taek,Chang, Se-Hun,Lee, Jae-Seoul,Cha, Yong-Hun,Oh, Ik-Hyun 한국재료학회 2007 한국재료학회지 Vol.17 No.6
[ $Mg_{97}Zn_1Y_2$ ] alloy powders were prepared from gas atomization process, followed by consolidation using spark plasma sintering (SPS) process. The atomized $Mg_{97}Zn_1Y_2$ alloy particles were entirely spherical in shape and dendritic microstructure. The compacts sintered by SPS process had theoretical density more than 99%. The compressive yield strength was decreased as sintering temperature increased. It was found that the compressive strength showed the maximum value of 303MPa at the $Mg_{97}Y_2Zn_1$ specimen sintered under load of 255 MPa at $350^{\circ}C$.
방전플라즈마 소결법에 의해 제조된 다공질 타이타늄 임플란트의 평가
오익현 ( Ik Hyun Oh ),손현택 ( Hyeon Taek Son ),장세훈 ( Se Hun Chang ),김형모 ( Hyung Mo Kim ),이기용 ( Ki Yong Lee ),박순섭 ( Sun Sub Park ),송호연 ( Ho Yeon Song ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.6
Porous Ti compacts were fabricated by spark plasma sintering (SPS) method and their Young`s modulus and biocompatibility were investigated in this study. Ti powders were made from commercially available pure Ti electrode (grade 2) using the plasma rotating electrode process (PREP) in an Ar atmosphere. Porous Ti compacts for biomedical applications were successfully fabricated in the porosity range from 5 to 36 vol%. Young`s modulus of porous Ti compacts having porosity from 31 to 36 vol % is almost the same as that of human cortical bone. To investigate the biocompatibility of pure Ti, fibroblast-like L-929 and osteoblast-like MG-63 cells were cultured with the presence of the extract solution from pure Ti powder and porous body. The viabilities of cells cultured with the diluted extract solutions were almost the same compared to that of the control. Also, porous Ti compacts did not induce any morphologic damage of cell.
교차롤압연된 Ni-10Cr 합금의 결정립 미세화와 성형성 향상
송국현,김원용,손현택,Song, Kuk-Hyun,Kim, Won-Yong,Son, Hyun-Taek 한국재료학회 2012 한국재료학회지 Vol.22 No.6
This study evaluated the enhancement of microstructural and mechanical properties of a cross rolled Ni-10Cr alloy, comparing with conventionally rolled material. Cold rolling was carried out to 90% thickness reduction and the specimens were subsequently annealed at $700^{\circ}C$ for 30 min to obtain a fully recrystallized microstructure. Cross roll rolling was carried out at a tilted roll mill condition of $5^{\circ}$ from the transverse direction in the RD-TD plane. In order to observe the deformed microstructures of the cold rolled materials, transmission electron microscopy was employed. For annealed materials after rolling, in order to investigate the grain boundary characteristic distributions, an electron back-scattering diffraction technique was applied. Application of cold rolling to the Ni-10Cr alloy contributed to notable grain refinement, and consequently the average grain size was refined from 135 ${\mu}m$ in the initial material to 9.4 and 4.2 ${\mu}m$ in conventionally rolled and cross rolled materials, respectively, thus showing more significantly refined grains in the cross rolled material. This refined grain size led to enhanced mechanical properties such as yield and tensile strengths, with slightly higher values in the cross rolled material. Furthermore, the <111>//ND texture in the CRR material was better developed compared to that of the CR material, which contributed to enhanced mechanical properties and formability.
송국현,김대근,손현택,이해진,김한솔,김원용,Song, Kuk-Hyun,Kim, Dae-Keun,Son, Hyun-Taek,Lee, Hae-Jin,Kim, Han-Sol,Kim, Won-Yong 한국재료학회 2011 한국재료학회지 Vol.21 No.10
We carried out this study to evaluate the grain refining in and the mechanical properties of alloys that undergo severe plastic deformation (SPD). Conventional rolling (CR) and cross-roll rolling (CRR) as SPD methods were used with Ni-20Cr alloy as the experimental material. The materials were cold rolled to a thickness reduction of 90% and subsequently annealed at $700^{\circ}C$ for 30 min to obtain a fully recrystallized microstructure. For the annealed materials after the cold rolling, electron back-scattered diffraction (EBSD) analysis was carried out to investigate the grain boundary characteristic distributions (GBCDs). The CRR process was more effective when used to develop the grain refinement relative to the CR process; as a result, the grain size was refined from $70{\mu}m$ in the initial material to $4.2{\mu}m$ (CR) and $2.4{\mu}m$ (CRR). These grain refinements have a direct effect on improving the mechanical properties; in this case, the microhardness, yield and tensile strength showed significant increases compared to the initial material. In particular, the CRR-processed material showed more effective values relative to the CR-processed materials. The different texture distributions in the CR (001//ND) and CRR (111//ND) were likely the cause of the increase in the mechanical properties. These findings suggest that CRR can result in materials with a smaller grain size, improved texture development and improved mechanical properties after recrystallization by a subsequent annealing process.
Ag첨가 마그네슘 합금의 이중열처리에 따른 미세조직 및 기계적 특성변화
이병덕 ( Byeong Deok Lee ),백의현 ( Ui Hyun Baek ),장경수 ( Kyoung Soo Jang ),한정환 ( Jeong Whan Han ),손현택 ( Hyeon Taek Son ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6
To improving the mechanical properties of Mg alloys at high temperature, we investigated the mechanical properties at high temperature and the change of microstructure of Mg-6 wt%Zn-0.4 wt%Mn and Mg-6 wt%Zn-0.4 wt%Mn-1 wt%Ag alloys on age treatment that have a stable MgZn phase at high temperature and AgMg4 improving yield stress. In order to predict thermodynamic data of Mg alloys, a phase diagram and precipitation phase were calculated using a thermodynamic program, and it was confirmed that the MgZn and AgMg4 phase existed as main precipitation in this alloys. The experimental data examined using DSC and XRD were comparable with the calculated data for reliability. In order to analysis the microstructure and precipitate phase during aging treatment, it was measured by SEM/EDS and TEM. Lastly, mechanical properties of the MgZn and AgMg4 phase were measured by a tensile test at high temperature.