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Application of Nanoindentation Technique for Characterizing Surface Properties of Carburized Materials (침탄 처리 소재의 표면 분석을 위한 나노압입시험법의 응용)

  • Choi, In-Chul;Oh, Myung-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.35 no.3
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    • pp.139-149
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    • 2022
  • In the automobile and shipbuilding industries, various materials and components require superior surface strength, excellent wear resistance and good resistance to repeated loads. To improve the surface properties of the materials, various surface heat treatment methods are used, which include carburizing, nitriding, and so on. Among them, carburizing treatment is widely used for structural steels containing carbon. The effective carburizing thickness required for materials depends on the service environment and the size of the components. In general, however, there is a limit in evaluation of the surface properties with a standardized mechanical test method because the thickness or cross-sectional area of the carburized layer is limited. In this regard, the nanoindentation technique has lots of advantages, which can measure the mechanical properties of the material surface at the nano and micro scale. It is possible to understand the relationship between the microstructural change in the hardened layer by carburizing treatment and the mechanical properties. To be spread to practical applications at the industrial level, in this paper, the principle of the nanoindentation method is described with a representative application for analyzing the mechanical properties of the carburized material.

Study on the Fatigue Resistance of Gray Cast Iron in CO2 Laser Surface Hardening (CO2레이저 표면경화(表面硬化) 처리된 회주철(灰鑄鐵)의 피로특성(疲勞特性)에 관한 연구(硏究))

  • Park, K.W.;Han, Y.H.;Lee, S.Y.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.3
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    • pp.169-181
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    • 1995
  • This study has been performed to investigate some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and fatigue resistance of gray cast iron treated by laser surface hardening technique. Optical micrograph has shown that the dissolution of graphite flakes and the coarsening of lath martensite tend to increase with a small amount of retained austenite as the power density increases under the condition of a given traverse speed. Hardness measurements have revealed that as the power density increases, hardness values of outermost surface layer increases from Hv=620 to Hv=647 in case of traverse speed of 2.0m/min at gray cast iron. Fatigue test has exhibited that the fatigue strength of laser surface hardened specimen is superier compared to that of untreated specimen, showing that values for the fatigue strength at Nf=107 of gray cast iron laser-surface-hardened at a low power density of 4076w/cm2 and a high power density of 8153w/cm2 under the condition of a given traverse speed of 2.0m/min are 15kgf/mm2 and 20kgf/mm2, respectively, whereas the fatigue strength of untreated specimen is 11kgf/mm2. Under high stress-low cycle condition a noraml brittleness fracture appears, whereas a ductile fracture with beach mark is observed in the specimen tested under low stress-high cycle condition.

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Effects of differently hardened brass foil laminate on the electromechanical property of externally laminated CC tapes

  • Bautista, Zhierwinjay;Shin, Hyung-Seop;Mean, Byoung Jean;Lee, Jae-Hun
    • Progress in Superconductivity and Cryogenics
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    • v.18 no.4
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    • pp.21-24
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    • 2016
  • The mechanical properties of REBCO coated conductor (CC) wires under uniaxial tension are largely determined by the thick component layers in the architecture, namely, the substrate and the stabilizer or even the reinforcement layer. Depending on device applications of the CC tapes, it is necessary to reinforce thin metallic foils externally to one-side or both sides of the CC tapes. Due to the external reinforcement of brass foils, it was found that this could increase the reversible strain limit from the Cu-stabilized CC tapes. In this study, the effects of differently hardened brass foil laminate on the electromechanical property of CC tapes were investigated under uniaxial tension loading. The tensile strain dependence of the critical current (Ic) was measured at 77 K and self-field. Depending on whether the Ic of CC tapes were measured during loading or after unloading, a reversible strain (or stress) limit could be determined, respectively. The both-sides of the Cu-stabilized CC tapes were laminated with brass foils with different hardness, namely 1/4H, 1H and EH. From the obtained results, it showed that the yield strength of the brass laminated CC tapes with EH brass foil laminate was comparable to the one of the Cu-stabilized CC tape due to its large yield strength even though its large volume fraction. It was found that the brass foil with different hardness was mainly sensitive on the stress dependence of Ic, but not on the strain sensitivity due to the residual strain induced in the laminated CC tapes during unloading.

Electron Discharge Machining (EDM) and Hole EDM of Cold Heat-treated Tool Steel Molds (STD11) by using Cu Electrodes (냉간 금형용 공구강의 Cu 전극을 이용한 방전 홀에 관한 연구)

  • Park, In-Soo;Lee, Eun-Ju;Kim, Hwa-Jeong;Wang, Deok-Hyun
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.17 no.4
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    • pp.76-82
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    • 2018
  • 3D formed Electrical Discharge Machining (EDM) and hole EDM were conducted for die and mold manufacturing with electrodes which were made by mechanical machining and wire EDM. It is difficult to machine the hardened material after heat treatment and quenching with traditional machining. The only method of machining hardened material is die-sinking EDM. In this research, hole EDM was conducted for heat-treated cold-worked tool steel (SKD11) for use as a die material. The EDM surfaces were analyzed by pulse-on time and peak current of EDM current, according to the machining conditions of EDM. The EDM surface profiles were affected by the peak current. The contribution of each factor is peak current (91.63%) and pulse-on time (0.93%). The best surface roughness was obtained with a 130μs pulse-on time and a 14.2 A peak current. With uniform EDM processing, the surface deteriorated with increasing pulse-on time and peak current. The thickness of the solidified layer induced by EDM was increased as the peak current, crater shapes, and erupted shapes of EDM surfaces were increased. Therefore, microcracking gaps induced by surface tension were increased.

Effect of Laser Surface Hardening Factors on the Wear Resistance of Medium Carbon Low Alloy Steel Surface-hardened by Using CO2 Laser Technique (CO2 레이저 표면경화처리된 중탄소 저합금강의 내마모 특성에 미치는 레이저 표면경화 인자의 영향)

  • Park, K.U.;Roh, Y.S.;Han, Y.H.;Lee, S.Y.
    • Journal of the Korean Society for Heat Treatment
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    • v.5 no.2
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    • pp.122-132
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    • 1992
  • This study has been performed to investigate into some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and wear characteristics of medium carbon low alloy steel treated by laser surface hardening technique. The results obtained from the experiment are summarized as follows : (1) Optical micrograph has shown that finer lath martensite is formed and the amount of undissolved complex carbides increases as the traverse speed increases under the condition of a given power density, whereas the coarsening of lath martensite and the reduction of undissolved complex carbides occur with increasing the power density at a given traverse speed. (2) Hardness measurements have revealed that as the traverse speed increases, hardness values of outermost surface layer more of less decrease under low power densities, but are uniformly distributed under high power densities, also showing that they are uniformly distributed at low traverse speeds and more or less decrease at high traverse speeds with increasing the power density. (3) The effective case depth has been found to decrease from 0.26 mm to 0.17 mm with increasing the traverse speed from 1.5 m/min to 3.0 m/min at a given power density of 25.48×103w/cm2 and to increase from 0.20 mm to 0.36 mm with increasing the power density from 19.11×103w/cm2 to 38.22×103w/cm2 at a given traverse speed of 2.0 m/min. (4) Wear test has exhibited that the amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load increases with increasing traverse speed at a given power density and decreses with increasing power density at a given traverse speed.

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Evaluation of Bonding Properties of Epoxy Solder Joints by High Temperature Aging Test (고온 시효 시험에 따른 Epoxy 솔더 접합부의 접합 특성 평가)

  • Kang, Min-Soo;Kim, Do-Seok;Shin, Young-Eui
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.32 no.1
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    • pp.6-12
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    • 2019
  • Bonding properties of epoxy-containing solder joints were investigated by a high temperature aging test. Specimens were prepared by bonding an R3216 standard chip resistor to an OSP-finished PCB by a reflow process with two basic types of solder (SAC305 & Sn58Bi) pastes and two epoxy-solder (SAC305+epoxy & Sn58Bi+epoxy) pastes. In all epoxy solder joints, an epoxy fillet was formed in the hardened epoxy, lying around the outer edge of the solder joint, between the chip and the Cu pad. In order to analyze the bonding characteristics of solder joints at high temperatures, a high-temperature aging test at 150C was carried out for 14 days (336 h). After aging, the intermetallic compound Cu6Sn5 was found to have formed in the solder joint on the Cu pad, and the shear stress on the conventional solder joint was reduced by a significant amount. The reason that the shear force did not decrease much, even though in epoxy solder, was thatbecause epoxy hardened at the outer edge of the supported solder joints. Using epoxy solder, strong bonding behavior can be ensured due to this resistance to shear force, even in metallurgical changes such as those where intermetallic compounds form at solder joints.

Microstructure and Mechanical Properties of AA6061/AA5052/AA6061 Complex Sheet Fabricated by Cold-Roll Bonding Process (냉간압연접합법에 의해 제조된 AA6061/AA5052/AA6061 복합판재의 미세조직 및 기계적 성질)

  • Hwang, Ju-Yeon;Lee, Seong-Hee
    • Korean Journal of Materials Research
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    • v.29 no.6
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    • pp.392-397
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    • 2019
  • A cold roll-bonding process is applied to fabricate an AA6061/AA5052/AA6061 three-layer clad sheet. Two AA6061 and one AA5052 sheets of 2 mm thickness, 40 mm width, and 300 mm length are stacked, with the AA5052 sheet located in the center. After surface treatment such as degreasing and wire brushing, sample is reduced to a thickness of 1.5 mm by multi-pass cold rolling. The rolling is performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 400 mm at rolling speed of 6.0 m/sec. The roll bonded AA6061/AA5052/AA6061 complex sheet is then hardened by natural aging(T4) and artificial aging(T6) treatments. The microstructures of the as-roll bonded and age-hardened Al complex sheets are revealed by optical microscopy; the mechanical properties are investigated by tensile testing and hardness testing. After rolling, the roll-bonded AA6061/AA5052/AA6061 sheets show a typical deformation structure in which grains are elongated in the rolling direction. However, after T4 and T6 aging treatment, there is a recrystallization structure consisting of coarse equiaxed grains in both AA5052 and AA6061 sheets. The as roll-bonded specimen shows a sandwich structure in which an AA5052 sheet is inserted into two AA6061 sheets with higher hardness. However, after T4 and T6 aging treatment, there is a different sandwich structure in which the hardness of the upper and lower layers of the AA6061 sheets is higher than that of the center of the AA5052 sheet. The strength values of the T4 and T6 age-treated specimens are found to increase by 1.3 and 1.4 times, respectively, compared to that value of the starting material.

The Effect of Fatigue Strength according to Carburizing Depth (침탄 두께에 따른 피로강도 영향 특성 평가)

  • Choi, Hyun Min;Park, Yong Ha;Shin, Yong Taek;Kim, Myung Hyun
    • Journal of Welding and Joining
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    • v.32 no.4
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    • pp.34-38
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    • 2014
  • Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

A Study on machining characteristics of the Electropolishing of Aluminum alloy (알루미늄 합금의 전해연마 가공특성에 관한 연구)

  • 이은상;김창근
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.12 no.2
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    • pp.17-22
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    • 2003
  • Electropolishing is the electrolytic removal of metal in a highly ionic solution by means of an electrical potential and current. It is normally used to remove a very thin layer of material on the surface of a metal part or component. Electropolishing is able to enhance the material properties of a workpiece and to change its physical dimensions. Also, It is suitable for the polishing of both complex shapes and hardened materials, which are difficult to machine mechanically. therefore, the aim of the present study is to investigate the characteristic of Electropolishing A12024 in terms of current density, polishing time and electrode gap, etc.

Radiation Hardness Evaluation of GaN-based Transistors by Particle-beam Irradiation (방사선빔 조사를 이용한 질화갈륨 기반 트랜지스터의 내방사선 특성 연구)

  • Keum, Dongmin;Kim, Hyungtak
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.9
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    • pp.1351-1358
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    • 2017
  • In this work, we investigated radiation hardness of GaN-based transistors which are strong candidates for next-generation power electronics. Field effect transistors with three types of gate structures including metal Schottky gate, recessed gate, and p-AlGaN layer gate were fabricated on AlGaN/GaN heterostructure on Si substrate. The devices were irradiated with energetic protons and alpha-particles. The irradiated transistors exhibited the reduction of on-current and the shift of threshold voltage which were attributed to displacement damage by incident energetic particles at high fluence. However, FET operation was still maintained and leakage characteristics were not degraded, suggesting that GaN-based FETs possess high potential for radiation-hardened electronics.