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극저온 열처리가 7075 알루미늄 합금의 잔류응력과 기계적 특성에 미치는 영향
김회봉,정은욱,고대훈,김병민,조영래,Kim, Hoi-Bong,Jeong, Eun-Wook,Ko, Dae-Hoon,Kim, Byung-Min,Cho, Young-Rae 한국재료학회 2013 한국재료학회지 Vol.23 No.1
In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at $470^{\circ}C$, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.
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극저온 열처리가 7075 알루미늄 합금의 잔류응력과 석출에 미치는 영향
김회봉 ( Hoi Bong Kim ),김동용 ( Dong Yong Kim ),고대훈 ( Dae Hoon Ko ),김병민 ( Byung Min Kim ),조영래 ( Young Rae Cho ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.5
To develop 7075 aluminum (Al7075) alloy with low residual stress and high strength, a modified cryogenic treatment was proposed. In this study, the effects of two additional steps on residual stress in Al7075 were investigated. Unlike the conventional age-hardening process, the first step of the modified treatment is cryogenic quenching, followed by the second step of uphill quenching of the samples. The mechanical properties and residual stress of samples were characterized by Vickers hardness and X-ray diffraction with sin2 method, respectively. Structural properties such as size and formation of the precipitates of the samples were characterized by transmission electron microscopy and electron energy loss spectroscopy. Three different uphill quenching methods, boiling water, room temperature water, and air, were applied to the samples. Samples treated by the boiling water uphill quenching method showed the lowest residual stress and highest hardness. Results clearly demonstrated that the modified cryogenic treatment with boiling water uphill quenching method was a very useful heat treatment to achieve an age-hardened Al7075 alloy with low distortion shape, low residual stress and high hardness.
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마그네트론 스파터시 금속 극박막의 실시간 전기저항과 미세구조 변화
권나현,김회봉,황빈,배동수,조영래,Kwon, Na-Hyun,Kim, Hoi-Bong,Hwang, Bin,Bae, Dong-Su,Cho, Young-Rae 한국재료학회 2011 한국재료학회지 Vol.21 No.3
Ultra-thin aluminum (Al) and tin (Sn) films were grown by dc magnetron sputtering on a glass substrate. The electrical resistance R of films was measured in-situ method during the film growth. Also transmission electron microscopy (TEM) study was carried out to observe the microstructure of the films. In the ultra-thin film study, an exact determination of a coalescence thickness and a continuous film thickness is very important. Therefore, we tried to measure the minimum thickness for continuous film (dmin) by means of a graphical method using a number of different y-values as a function of film thickness. The raw date obtained in this study provides a graph of in-situ resistance of metal film as a function of film thickness. For the Al film, there occurs a maximum value in a graph of in-situ electrical resistance versus film thickness. Using the results in this study, we could define clearly the minimum thickness for continuous film where the position of minimum values in the graph when we put the value of Rd3 to y-axis and the film thickness to x-axis. The measured values for the minimum thickness for continuous film are 21 nm and 16 nm for sputtered Al and Sn films, respectively. The new method for defining the minimum thickness for continuous film in this study can be utilized in a basic data when we design an ultra-thin film for the metallization application in nano-scale devices.
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잉곳 슬라이싱용 Saw Wire의 연삭마모에 미치는 인장특성과 미세조직의 영향
황빈,김동용,김회봉,임승호,임재덕,조영래,Hwang, Bin,Kim, Dong-Yong,Kim, Hoi-Bong,Lim, Seung-Ho,Im, Jae-Duk,Cho, Young-Rae 한국재료학회 2011 한국재료학회지 Vol.21 No.6
Saw wires have been widely used in industries to slice silicon (Si) ingots into thin wafers for semiconductor fabrication. This study investigated the microstructural and mechanical properties, such as abrasive wear and tensile properties, of a saw wire sample of 0.84 wt.% carbon steel with a 120 ${\mu}M$ diameter. The samples were subjected to heat treatment at different linear velocities of the wire during the patenting process and two different wear tests were performed, 2-body abrasive wear (grinding) and 3-body abrasive wear (rolling wear) tests. With an increasing linear velocity of the wire, the tensile strength and microhardness of the samples increased, whereas the interlamellar spacing in a pearlite structure decreased. The wear properties from the grinding and rolling wear tests exhibited an opposite tendency. The weight loss resulting from grinding was mainly affected by the tensile strength and microhardness, while the diameter loss obtained from rolling wear was affected by elongation or ductility of the samples. This result demonstrates that the wear mechanism in the 3-body wear test is much different from that for the 2-body abrasive wear test. The ultra-high tensile strength of the saw wire produced by the drawing process was attributed to the pearlite microstructure with very small interlamellar spacing as well as the high density of dislocation.
ScienceON
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