• Title/Summary/Keyword: substitutional elements

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Effect of Al Content Variation on High Temperature Gas Nitriding in 13%Cr-0.16%C Stainless Steel (13%Cr-0.17%C 스테인리스강의 고온 가스질화에 미치는 Al 함량 변화의 영향)

  • Park, B.T.;Kim, J.M.;Kang, H.J.;Kong, J.H.;Kang, C.Y.;Sung, J.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.6
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    • pp.318-326
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    • 2011
  • This study has been performed to investigate the effect of Al addition on High Temperature Gas Nitriding (HTGN) in 13%Cr-0.16%C stainless steel with different Al contents of 0.54%, 1.76% and 2.36%, respectively. HTGN treatment was carried out at $1100^{\circ}C$ for 1 hr, 5 hrs and 10 hrs. Nitrogen-permeated surface layers showed round type carbides of $Cr_{23}C_6$ and needle type nitrides of AlN in the matrix of martensite, representing 600~700 Hv. And the thickness of the surface layer increased with increasing Al content and HTGN treatment time. The inner region that was not permeated nitrogen showed chromium carbides in the mixed phase of martensite and ferrite for the 0.53% Al alloyed steel, however chromium carbides in the matrix of ferrite single phase were shown for the steels with the addition of 1.76%Al and 2.36%Al, representing the hardness of ~200 Hv. During nitrogen permeation from surface to the interior, substitutional elements of Cr, Al and Si moved toward the surface and interstitial element of carbon also moved from interior to the surface. This movement of alloying elements leads high concentration of these elements at the outmost surface, subsequently the lowest peak of substitutional elements were shown in the vicinity of near surface. After showing the lowest peak, the high concentration region of Al and C were formed due to the continuous movement of Al toward the surface. The long discontinuous precipitates of $Cr_{23}C_6$ and AlN were formed along the outmost surface owing to the high concentration of these alloying elements.

Effects of Alloy Additions and Annealing Parameters on Microstructure in Cold-Rolled Ultra Low Carbon Steels (극저탄소 냉연강판에서 합금원소 및 어닐링조건이 미세조직에 미치는 영향)

  • Jeong, Woo Chang
    • Journal of the Korean Society for Heat Treatment
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    • v.17 no.2
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    • pp.78-86
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    • 2004
  • Effects of the annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.

Effects of Ni addition on continuous cooling transformation behavior of low carbon HSLA steels (저탄소${\cdot}$저합금 강의 연속 냉각 변태에 미치는 Ni의 영향)

  • Kang J. S.;Jun J. H.;Park C. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.456-459
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    • 2005
  • Continuous cooling transformation behaviors were studied fur low carbon HSLA steels containing three different level $(1\~3\;wt\%)$ of Ni addition. Thermo-mechanical processing (TMP) simulations to construct continuous cooling (CCT) diagram were conducted by using Gleeble system. As cooling rate increased, pearlite, granular bainite, acicular ferrite, bainitic ferrite and lath martensite were transformed from deformed austenite. Fully bainitic microstructure were developed at all cooling rate condition in high Ni containing steel due to hardenability increasing effects of Ni. Ni also influenced the transformation kinetics. At the slowest cooling rate of $0.3^{\circ}C/s$, transformation delayed with decreasing Ni contents because of the diffusion of substitutional alloy elements. However, cooling rate slightly increased to $1^{\circ}C/s$, transformation kinetics accelerated with decreasing Ni contents because nucleation of bainite was sluggish due to hardening of residual austenite.

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Sintering of Alloyed $Ni_3Al$ Starting from Mechano-composites Powders

  • Lucaci, Mariana;Orban, Radu L.;Lungu, Magdalena;Enescu, Elena;Gavriliu, Stefania
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1234-1235
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    • 2006
  • Considering the idea that some properties, especially the mechanical properties of $Ni_3Al$ at ambient temperature can be improved by adding of some substitutional/interstitial elements, our goal was to obtain these materials starting from mechano-composites powders. In this aim, using mechanical alloying techniques three type of mechano-composite powders starting from elemental powders were obtained. Then, by reactive sintering in argon atmosphere at temperature over $900^{\circ}C$, alloyed $Ni_3Al$ materials were realized. This paper presents our research results regarding the microstructural aspects and phase formation in obtained materials.

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A Novel Method to Calculate the Carbides Fraction from Dilatometric Measurements During Cooling in Hot-Work Tool Steel

  • Zhao, Xiaoli;Li, Chuanwei;Han, Lizhan;Gu, Jianfeng
    • Metals and materials international
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    • v.24 no.6
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    • pp.1193-1201
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    • 2018
  • Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversional model was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms after precipitation is considered as the only element that affects the lattice constant and the content of the alloy elements such as Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changes caused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope and transmission electron microscope. The relationship between lattice constant of carbides and temperature are measured by high-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different rates are V-rich MC and Cr-rich $M_{23}C_6$, and most of them are V-rich MC, only very few are Cr-rich $M_{23}C_6$. The model including the effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lower cooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematical model agree well.

Effect of Small Additives on the Microstructure of Strip-Cast Nd-Fe-B Alloys (소량의 첨가원소가 Strip-Cast Nd-Fe-B 향금의 미세 조직 형성에 미치는 영향)

  • Lee, D.H.;Jang, T.S.;Kim, D.H.;Kim, Andrew-S.
    • Journal of the Korean Magnetics Society
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    • v.14 no.5
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    • pp.196-200
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    • 2004
  • In order to improve dendritic formation of Nd$_2$Fe$\_$14/B phase in the strip-cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, effect of small substitutional additives such as Cu (0.3~1.0 at. %) and Co (0.5~1.5 at.%) on the phase formation and microstructures of the strip-cast alloys based on Nd$\_$14/Fe$\_$80/B$\_$6/ were investigated. As the amount of Cu addition increased, formation of Nd$_2$Fe$\_$14/B dendrites along the direction normal to the strip surface was suppressed with the reduction of the strip thickness mainly due to the increase of fluidity of the melt. However, both the dendrites and their <001> preferred orientation along the direction normal to the strip surface were improved with the increase of the strip thickness as the amount of Co addition increased. The dendrites became finer after small amount of Cu or Co was added. While small copper additions tended to stabilize the formation of primary Fe, small cobalt additions suppressed it. When small amount of Zr was added, however, the dendrite structures were totally collapsed with excessive grain growth of Nd$_2$Fe$\_$14/B.

A Study on Ion Exchange Method for Effective Ag Doping of Sputtering-Deposited CdTe Thin Film (스퍼터링 증착한 CdTe 박막의 효과적인 Ag 도핑을 위한 이온 교환법 연구)

  • Kim, Cheol-Joan;Park, Ju-Sun;Lee, Woo-Sun
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.60 no.6
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    • pp.1169-1174
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    • 2011
  • CdTe thin-film solar cell technology is well known that it can theoretically improve its conversion efficiency and manufacturing costs compared to the conventional silicon solar cell technology, due to its optical band gap energy (about 1.45eV) for solar energy absorption, high light absorption capability and low cost requirements for producing solar cells. Although the prior studies obtained the high light absorption, CdTe thin film solar cell has not been come up to the sufficient efficiency yet. So, doping method was selected for the improvement of the electrical characteristics in CdTe solar cells. Some elements including Cu, Ag, Cd and Te were generally used for the p-dopant as substitutional acceptors in CdTe thin film. In this study, the sputtering-deposited CdTe thin film was immersed in $AgNO_3$ solution for ion exchange method to dope Ag ions. The effects of immersion temperature and Ag-concentration were investigated on the optical properties and electrical characteristics of CdTe thin film by using Auger electron spectroscopy depth-profile, UV-visible spectrophotometer, and a Hall effect measurement system. The best optical and electrical characteristics were sucessfully obtained by Ag doping at high temperature and concentration. The larger and more uniform diffusion of Ag ions made increase of the Ag ion density in CdTe thin film to decrease the series resistance as well as mede the faster diffusion of light by the metal ions to enhance the light absorption.

High Temperature Gas Nitriding of Fe-20Mn-12Cr-1Cu Damping Alloy (Fe-20Mn-12Cr-1Cu 제진합금의 고온가스 질화처리)

  • Sung, Jee-Hyun;Kim, Yeong-Hee;Sung, Jang-Hyun;Kang, Chang-Yong
    • Journal of the Korean Society for Heat Treatment
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    • v.26 no.3
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    • pp.105-112
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    • 2013
  • The microstructural changes of Fe-20Mn-12Cr-1Cu alloy have been studied during high temperature gas nitriding (HTGN) at the range of $1000^{\circ}C{\sim}1150^{\circ}C$ in an atmosphere of nitrogen gas. The mixed microstructure of austenite and ${\varepsilon}$-martensite of as-received alloy was changed to austenite single phase after HTGN treatment at the nitrogen-permeated surface layer, however the interior region that was not affected nitrogen permeation remained the structure of austenite and ${\varepsilon}$-martensite. With raising the HTGN treatment temperature, the concentration and permeation depth of nitrogen, which is known as the austenite stabilizing element, were increased. Accordingly, the depth of austenite single phase region was increased. The outmost surface of HTGN treated alloy at $1000^{\circ}C$ appeared Cr nitride. And this was in good agreement with the thermodynamically calculated phase diagram. The grain growth was delayed after HTGN treatment temperature ranges of $1000^{\circ}C{\sim}1100^{\circ}C$ due to the grain boundary precipitates. For the HTGN treatment temperature of $1150^{\circ}C$, the fine grain region was shown at the near surface due to the grain boundary precipitates, however, owing to the depletion of grain boundary precipitates, coarse grain was appeared at the depth far from the surface. This depletion may come from the strong affinity between nitrogen and substitutional element of Al and Ti leading the diffusion of these elements from interior to surface. Because of the nitrogen dissolution at the nitrogen-permeated surface layer by HTGN treatment, the surface hardness was increased above 150 Hv compared to the interior region that was consisted with the mixed microstructure of austenite and ${\varepsilon}$-martensite.

Thre Relationaship of Scientific Knowledge and Ethical Value in Environmental Education (환경교육에서 과학적 지식과 윤리적 가치의 관계)

  • 김정호
    • Hwankyungkyoyuk
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    • v.10 no.2
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    • pp.51-62
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    • 1997
  • The objective of this study was to review the meaning and problems of Scientific Knowledge and Ethical Value in Environmental Education. The ultimate goal of environmental education is shaping proenvironmental human behavior. The factors of human behavioral decision making are ideology, value, attitude and behavioral intentions. Ideology is a kind of belief system used by social groups to interpret their social world. The main elements of belief system are knowledge and value. The traditional thinking in education has been that we can change behavior by making human beings more knowledgeable and more valuable. In environmental education, the aim of scientific inquiry is to analysis cause-effect relation of human beings behavior and environmental phenomenon, and ethical education is to change the mind of human beings from zero-sum to positive-sum about the relations between human beings and natural environments. But, there are many problems of knowledge education and value education in environmental education. For example scientific knowledge without ethical value is dangerous to environment protection, and ethical value without scientific knowledge is vague. Therefore, we must recognize that the relationship of ethical value and scientific knowledge is not substitutional but complementary. The teaching-learning methods which can integrate knowledge and value in environmental education are rational decision making model. For this model, we can construct teaching contents with inquiry materials. To earn the benefits of specialization among several subjects in environmental education, social studies can focus on social science knowledge and decision making, science education can focus on pure natural science knowledge and scientific investigation, moral education can focus on problems of ethical value system, home economics can focus on practical action and environmental education(Environments in middle school, Ecology and Environments in high school) can integrate social-national science knowledge and ethical value in broad perspective about human beings and ecosystem. That is the method to protect from law of diminishing marginal utility of learning in environmental education.

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Control of electrical types in the P-doped ZnO thin film by Ar/$O_2$ gas flow ratio

  • Kim, Young-Yi;Han, Won-Suk;Kong, Bo-Hyun;Cho, Hyung-Koun;Kim, Jun-Ho;Lee, Ho-Seoung
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.11a
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    • pp.11-11
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    • 2008
  • ZnO has a very large exciton binding energy (60 meV) as well as thermal and chemical stability, which are expected to allow efficient excitonic emission, even at room temperature. ZnO based electronic devices have attracted increasing interest as the backplanes for applications in the next-generation displays, such as active-matrix liquid crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs), and in solid state lighting systems as a substitution for GaN based light emitting diodes (LEDs). Most of these electronic devices employ the electrical behavior of n-type semiconducting active oxides due to the difficulty in obtaining a p-type film with long-term stability and high performance. p-type ZnO films can be produced by substituting group V elements (N, P, and As) for the O sites or group I elements (Li, Na, and K) for Zn sites. However, the achievement of p-type ZnO is a difficult task due to self-compensation induced from intrinsic donor defects, such as O vacancies (Vo) and Zn interstitials ($Zn_i$), or an unintentional extrinsic donor such as H. Phosphorus (P) doped ZnO thin films were grown on c-sapphire substrates by radio frequency magnetron sputtering with various Ar/ $O_2$ gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio with out post-annealing. The P-doped ZnO films grown at a Ar/ $O_2$ ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of $10^{-17}cm^{-3}$ and $2.5cm^2/V{\cdot}s$, respectively. X-ray diffraction showed that the ZnO (0002) peak shifted to lower angle due to the positioning of $p^{3-}$ ions with a smaller ionic radius in the $O^{2-}$ sites. This indicates that a p-type mechanism was due to the substitutional Po. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction LEO showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.

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