Study on Microstructure and Mechanical Properties of the Al–25Cr–5Si (at%) Alloy Powder Using Gas-Atomization and SPS Process

Yong‑Ho Kim,Hyo‑Sang Yoo,Jeong‑Han Lee,Ik‑Hyun Oh,Hyun‑Kuk Park,Hyeon‑Taek Son 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

In order to investigate the microstructure and mechanical properties on Al–25Cr–5Si (at%) alloy, a mixed powder with pureelements and an alloy powder using a gas atomization process were used. Fine and high purity Al–25Cr–5Si (at%) alloypowder was successfully prepared by gas atomization and densified using a spark plasma sintering (SPS) process. The overallpowder size distribution of the mixed Al, Cr, and Si elemental powders was in the range of 10–15 μm. The atomized Al–Cr–Sialloy powder was fine and spherical in morphology and difficult to be formed by intermetallic formation. Densification wasclearly confirmed at 1000 °C, with almost isolated pores formed, by clear removal of pores between particles, deformationof particles, an increase in the number of contacts, and a change in size between particles. As a result of XRD analysis ofthe sintered compacts, single phase was observed using the mixed powder, but the compact using gas atomization remainedthe alloy phase even at the process temperature. The Vickers hardness of the compacts by mixed powder was observed at59.70 Hv and the compact using gas atomized powders on the temperature 1000 °C of the Vickers hardness increased to702.6 Hv. The compressive yield strength of the compact with mixed powder was 195.24 MPa and the compressive strengthof the compact with gas atomized powder increased to 802.07 MPa. It is considered not to be decomposed by the AlCrSi,Al13Cr4Si4and Al8Cr5phases sintering process, resulting from the improvement of mechanical properties.

보이드 생성기구에 의한 복합조직강의 연성 파괴거동에 관한 연구

吳澤烈,崔明振,楡龍錫,金松正 慶熙大學校 材料科學技術硏究所 1993 材料科學技術硏究論集 Vol.6 No.-

Ductile Fracture of Dual Pase Steel begins with void nucleation, at Martensite-Ferrite interface or deformed Martensite particle. In this study void nucleation, void growth, void volume fraction and void coalescence at given strain were studied in dual phase steel. Therefore, by means of the heat treatment of low corbon steel the study deal with void nucleation and void growth for ferrite grain sizeof dual phase steel. Void nucleaton and void growth with increasing strain are shown depend upon the ferrit grain size. The number of voids and volume fraction of voids generary increase as ferrite grain size decrease. At the close to fracture the void coalescence in the direction of the applied tensile stress, but near the fracture surface they linked in direction transverse to the tensile axis.

전력계통의 모선분할에 대한 단락용량 해석방법 연구

오용택 韓國技術敎育大學校 1995 論文集 Vol.2 No.1

Short circuit analysis is one of the most fundamental procedures for power system analysis problem. The problem related to short circuit studies should be requested greater interest to the future, especially in terms of power system availability and reliability. In order to solve the problem, it's required to develop an advanced algorithm by which short circuit currents are easily computed for a large number of alternative network configurations at main substation. This paper proposes a new calculation method to efficiently modify the bus impedance matrix elements to short circuit studies for bus separation in large power system by method of addition and removal of dummy link, and presents its practicality by applying the proposed method to the calculation short circuit analysis in the power system model.

초내식성 스테인리스강 선재와 브라켓의 내식성 및 금속 이온 용출 특성

오근택,정경진,황충주,박용수,김경남 大韓齒科器材學會 2001 대한치과재료학회지 Vol.28 No.4

Metallic orthodontic appliances are known to release metal ions in an oral cavity. It is not advisable that toxic corrosion products derived from the appliances is absorbed into the body. Metal ions release from orthodontic appliances is known to have large effects on the result of orthodontic treatment and systemic health. Metal bracket and wire were made of super stainless steel(S32050) with high corrosion resistance. The corrosion resistance and ion release property of S32050 and conventionally used appliances were examined. Four types of wire were ligated in either super stainless steel(SB) or Tomy bracket(TB) with O-ring, and then each group was immersed in an artificial saliva at 37℃ for 12 weeks. Amount of released metal ions was measured with immersion time by graphite furnace atomic absorption spectroscopy and surface morphology was investigated. S32050 showed the low passive current density of about 1 μA/㎠ and the stable passive region to a high potential in artificial saliva. S32050 appliances did hardly release nickel ions in artificial saliva. S32050 wire(SRW) and NiTi wire(NW) didn't show significant difference of Ni ion release with immersion time, meanwhile, Remanium wire(RW) showed significant difference in 12 weeks. Ni ion releasce from the brackets didn't show any significant difference with immersion time and between SB and TB. Amounts of Ni ion released from TB-SRW showed significant difference in 12 weeks, those from TB-RW showed significant difference from 4 weeks later and highest release among all groupsin12weeks. TB-NW released little Ni ion for all immersion time and showed significant difference from 4 weeks later, TB-TW(TMA wire) showed significant difference in 12 weks. SB-SRW didn't show any significant difference and SB-RW signigicant difference in 12 weeks,but lower compared with TB group. SB-NW and SB-TW didn't show any significant difference. Corrosion products didn't be observed in mostly groups during the immersion time, except that in TB-RW, they were observed on the bracket surface between O-ring and wire from 8 weeks later. Super stainless steel wire had good corrosion resistance compared with stainless steel wire, and it is believed that it can be used as orthodontic material for bracket and wire.

교정용 스테인리스강 선재의 내식성에 미치는 응력 제거 열처리 조건의 영향

오근택,전용석,황충주,김경남 대한치과기재학회 2001 대한치과재료학회지 Vol.28 No.2

Heat treatment is applied to orthodontic wires in order to relieve the stress that results from cold working and the orthodontists manipulations. In this study, 4 types of wires were heat-treated in an air, argon or vacuum environment, and were either cooled in a furnace or a water bath. Corrosion properties of the heat-treated wires were investigated by potentiodynamic method. The difference of corrosion resistance between the wires heat-treated in an ambient according to cooling methods was not significant. After heat-treated in an ambient, both water-cooled and furnace-cooled wires had a similar and low corrosion resistance. The difference of corrosion resistance between the wires heat-treated n a vacuum environment with cooling methods was significant. After heat-treated in a vacuum, the furnace-cooled wires had high corrosion resistance, but the water-cooled wires low. After heat-treated in a vacuum, argon, or air environments, the water-cooled wires had low corrosion resistance. It was considered because the irregular and unstable film was formed on the surface of the wires when cooled in a water bath. The control wires showed a low current density and high pitting potential, but most of the heat-treated wires did high current density and low pitting potential except for the wire heat-treated in vacuum and then cooled in a furnace. Conclusively, orthodontic wires are considered to have to be heat treated in vacuum condition or inert gas environment and then to be cooled in a furnace in order to inhibit surface oxidation, minimize the decrease of corrosion resistance and improve the mechanical properties.

교정학적 적용을 위한 초내식성 스테인리스강의 특성

오근택,김금진,황충주,박용수,김경남 大韓齒科器材學會 2001 대한치과재료학회지 Vol.28 No.3

Various kinds of orthodontic appliances have been developed for ideal tooth movement during orthodontic treatment. The orthodontic appliances made of metals are bands, arch wires, brackets and miniscrews as orthodontic anchorage. Generally, these appliances are made of stainless steel, pure titanium, Ni-Ti and TMA with the proper biocompatibility. However, localized corrosion of these materials can frequently occur in the particular environment. Super stainless steels, recently developed, have good corrosion resistance to reduce metal ion release induced by many kinds of corrosion. Recently, it has been reported that nickel ion release from orthodontic appliances affect the prevalence of nickel sensitization; however, there has been some controversy about nickel hypersensitivity to orthodontic appliances containing nickel. The purpose of this study was to evaluate and compare the microhardness, nickel ion release, corrosion resistance and cytotoxicity of 4 types of super stainless steels and 316L stainless steel as the control group according to nickel contents, and to determine the acceptability as the new material for various kinds of orthodontic appliances. All super stainless steels showed higher microhardness than 316L stainless steel, SR-3Mo showed especially the highest microhardness. In anodic polarization test, corrosion resistance was high in order of SR-50A, SFSS, SR-6DX, 316L stainless steel, SR-3Mo. There was no increase in nickel ion release from SR-50A, SR-6DX, 316L stainless steel with immersion time in artificial saliva; whereas there was some increase from SFSS and SR-3Mo with immersion time. All super stainless steels showed very low cytotoxicity regardless of nickel contents although SR-3Mo showed relatively higher cytotoxicity than the others. It is concluded that SR-50A among super stainless steels has the highest corrosion resistance and biocompatibility. It is undesirable to consider the alloys with high nickel content to release lots of nickel ion.

골내 고정 장치용 초내식성 오스테나이트 및 듀플렉스 스테인리스강 가공재의 특성

오근택,강국진,박용수,김경남 大韓齒科器材學會 2003 대한치과재료학회지 Vol.30 No.3

Nickel is one of the most common causes of allergic contact dermatitis and hypersensitivity. In case of stainless steel as biomaterials, the higher the corrosion resistance and the lower the nickel content, the better it is or the human body. However, because nickel plays an essential role in the stabilization of the austenitic phase and the corrosion resistance of stainless steel, it is difficult to remove the nickel from the constituents of stainless steels completely. Therefore, the purpose of this study was to investigate corrosion resistance, cytotoxicity, and mechanical property of super stainless steels, which had high corrosion resistance by synergistic effect of Mo(or W) and N, with respect to nickel content and to evaluate their potential for orthodontic applications. Super austenitic stainless steel(SR-50A) had high nickel content of 22% and super duplex stainless steels nickel contents of 6~10%. Super austenitic and duplex stainless steels had nitrogen contents of above 0.2%. Also, these steels had high Mo or W contents which were able to increase the localized corrosion resistance. In terms of hardness, super stainless steels, which had Vickers hardness values of 374~400 Hv in cold-rolled state and 186~285 Hv in annealed state, exhibited higher values than 316L S. S.. Duplex stainless steels exhibited higher mechanical properties than austenitic stainless steels. In terms of corrosion resistance, super stainless steels exhibited lower passive current density(2.3~3.8 ㎂/cm^2) than pure Ti(6.6㎂/cm^2) in the body-simulated solution and similar potentiodynamic polarization behaviors. Pitting corrosion occurred in 316L S. S. but not in the others. Thus these steels were considered to have high corrosion resistance in the human body. In terms of cytotoxicity, SR-5OA and SAF2507 exhibited none cytotoxicity and the others slight. This results indicated that the cytotoxicity of alloys containing nickel had no relation with nickel content because SR-5OA with the highest nickel content exhibited none cytetoxicity In conclusion, it is considered that super stainless steels with high corrosion resistance and good biocompatibility can be used for orthodontic applications because of the enhanced passive film by high addition of Mo, W, N, etc.

상수처리 시스템에서의 막분리 공정의 개발

오중교,이태진,정두식,이용택 경희대학교 환경연구소 1995 環境硏究 論文集 Vol.6 No.-

Membrane filtration process seems to have many advantages such as improvement of drinking water quality, saving water purification chemicals and operation cost, easier operation and maintenance and saving time and cost for construction of a water purification plant. A study was conducted to optimize the use of a membrane process to produce potable water from Lake water in singal, Kyungkido, South Korea. We try to optimize the process by adjusting different pretreatment, various MWCO(Molecular Weig염(salt), alignate와 같은 천연고분자 또는 ht cut-off), hydrauric conditions.

회전익 항공기용 외활형식 착륙장치의 정ㆍ동적 분석에 관한 연구

유용석,이동명,채경덕,오택열 경희대학교 산학협력기술연구원 1996 산학협력기술연구논문집 Vol.2 No.-

It is important to make sure of design's reasonability concerning of structural vibration problems and safety with fulfilling the research and with analyzing the body structures that include the landing gear which has dynamic significant characteristics in helicopter, and to make systematical procedure which obtains engineering data to guarantee the quality of the helicopter that was developed by testing of parts, subsystems and body. In this study, Analysis of landing gear under FAR regulations was attempted, and systematical procedure for static and dynamic characteristics of the landing gear in many subsystems of the helicopter was classified.

호기성 생물막 여과법을 이용한 제지산업 폐수의 처리 특성

이태진,오중교,이용택,정두식 경희대학교 환경연구소 1995 環境硏究 論文集 Vol.6 No.-

This work researched the treatment characterization of paper mill waste water for Biological Aerated Filter (BAF)system. BAF process is ideal for reclamation and reuse of wastewater. It features excellent removal of organic matter and SS, Especially. it is easy maintain and achieves energe-saving and space-conservation when compared to conventionnal activated sludge method. This study resulted that upflow BAF system showed superior treatment efficiency to downflow one. The removal efficiencies of BOD, COD, SS were 85%, 80, 90%, respectively.