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- 검색키워드
- 저자 : ( Changhee Lee ) (검색결과 535 건)
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Correlation Between Constituent Phase and Weld Metal Properties in Ni-Reduced Duplex Stainless Steel
Youngchai Lee,Jae Hee Lee,Joonoh Moon,Tae‑Ho Lee,Changhee Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8
The intrinsic properties of austenite and ferrite on the mechanical properties and corrosion resistance of the duplex stainlesssteel weld metals was studied by substituting Ni with Mn, N, and Mn + N. The properties of the weldments fabricated throughgas tungsten arc welding (GTAW) were evaluated using tensile test, Vickers hardness, and potentiodynamic polarizationtests. The mechanical properties and corrosion resistance of the constituent phases were measured using nanoindentationand electron probe microanalysis, respectively. The austenite and ferrite phase fractions of the weld metal were maintainedat approximately 50:50, and no harmful phases degraded the properties. Excessive Mn decreased the corrosion resistance; alarge difference in corrosion resistance between austenite and ferrite also decreased the overall corrosion resistance. In thefiller metal in which Ni was replaced with only Mn or N, the austenite became harder than ferrite, as a result cracks initiatedinside the austenite. The tensile test showed that austenite, which became a relatively hard phase compared to ferrite accordingto the chemical composition, increased the yield strength and decreased the elongation of the weld metal.
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Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC+NiCr
Lee, Changmin,Park, Hyungkwon,Yoo, Jaehong,Lee, Changhee,Woo, WanChuck,Park, Sunhong Elsevier 2015 APPLIED SURFACE SCIENCE - Vol.345 No.-
<P><B>Abstract</B></P> <P>Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC+NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55wt% stellite#6 and 45wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures combined with the crack initiation sites such as the fractured WC particles, pores and solidification cracks. WC particles directly caused clad cracks by particle fracture under the tensile stress. The pores and solidification cracks also affected as initiation sites and provided an easy crack path ways for large brittle fractures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Major problem, clad cracking in laser cladding process, was researched. </LI> <LI> Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. </LI> <LI> Relationship between the residual stress and crack initiation was showed clearly. </LI> <LI> Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. </LI> <LI> Initiation sites of generating clad cracks were specifically studied in MMC coatings. </LI> </UL> </P>
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Reemergence of porcine epidemic diarrhea virus on Jeju Island
Lee, Sunhee,Ko, Deok-Ho,Kwak, Seong-Kyu,Lim, Chung-Hun,Moon, Sung-Up,Lee, Du Sik,Lee, Changhee The Korean Society of Veterinary Science 2014 大韓獸醫學會誌 Vol.54 No.3
Porcine epidemic diarrhea virus (PEDV) strains responsible for recent outbreaks in the United States have been occurring in Mainland Korea since late 2013. Over the past 10 years, PEDV outbreaks have not been reported on Jeju Island. However, in late March of 2014, PEDV re-emerged on Jeju Island and was found to be genetically identical to PEDV strains currently circulating in Mainland Korea. The present study was conducted to provide a better understanding of the epidemiology of PEDV and more effective preventive measures against PED.
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Graphene–nanowire hybrid structures for high-performance photoconductive devices
Lee, Hyungwoo,Heo, Kwang,Park, Jaesung,Park, Yongju,Noh, Seunguk,Kim, Kwang S.,Lee, Changhee,Hong, Byung Hee,Jian, Jikang,Hong, Seunghun The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.17
<P>Graphene–CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene–CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones. Our graphene–CdS NW structures can be useful because they were much faster than commercial CdS film-based photodetectors and had photocurrents large enough for practical applications.</P> <P>Graphic Abstract</P><P>We have developed a photoconductive channel based on graphene–CdS nanowire hybrid structures which exhibited large photocurrent and fast recovery speed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm16565a'> </P>
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Lee, Hyunkoo,Kang, Chan-Mo,Park, Myeongjin,Kwak, Jeonghun,Lee, Changhee American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.6
<P>We demonstrated highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) using tin dioxide (SnO<SUB>2</SUB>) nanoparticles (NPs) as an electron injection layer at the interface between the indium tin oxide (ITO) cathode and the organic electron transport layer. The SnO<SUB>2</SUB> NP layer can facilitate the electron injection since the conduction band energy level of SnO<SUB>2</SUB> NPs (−3.6 eV) is located between the work function of ITO (4.8 eV) and the lowest unoccupied molecular orbital (LUMO) energy level of typical electron transporting molecules (−2.5 to −3.5 eV). As a result, the IBOLEDs with the SnO<SUB>2</SUB> NPs exhibited a decrease of the driving voltage by 7 V at 1000 cd/m<SUP>2</SUP> compared to the device without SnO<SUB>2</SUB> NPs. They also showed a significantly enhanced luminous current efficiency of 51.1 cd/A (corresponds to the external quantum efficiency of 15.6%) at the same brightness, which is about two times higher values than that of the device without SnO<SUB>2</SUB> NPs. We also measured the angular dependence of irradiance and electroluminescence (EL) spectra in the devices with SnO<SUB>2</SUB> NPs and found that they had a nearly Lambertian emission profile and few shift in EL spectrum through the entire viewing angles, which are considered as remarkable and essential results for the application of OLEDs to display devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-6/am302787y/production/images/medium/am-2012-02787y_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am302787y'>ACS Electronic Supporting Info</A></P>
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Lee, Changhee,You, Jangyoul,Park, Hyeonku Elsevier 2018 Energy and buildings Vol.172 No.-
<P><B>Abstract</B></P> <P>In this study, we analyzed the thermal conductivity characteristics of a well-type underground heat exchanger with respect to the amount of injected heat per meter. Although a constant amount of heat was injected into the system, we compared and analyzed data for different borehole depths. We compared three different injection heat values (250, 300, and 350 W/m). We also analyzed the effective thermal conductivity with respect to different initial ignoring times (2 h, 3 h, and 5 h) based on different rock types and borehole depths. We did not observe a linear relationship between the rock types (alluvium, gneiss, and granite) and the borehole depth. The results suggest that different rock types have different thermal conductivity characteristics and the variation in the results is likely caused by groundwater, which affects the thermal conductivity measurements. For future geothermal heat exchanger designs, it is imperative to select a specific value for heat flow and an appropriate injection heat value depending on the rock type.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We analyzed the thermal conductivity of a well-type underground heat exchanger. </LI> <LI> We compared data for different borehole depths at 3 injection heat values. </LI> <LI> We analyzed effective thermal conductivity by 3 initial ignoring times. </LI> <LI> There is no linear relationship between rock types and the borehole depth. </LI> <LI> Different rock types have different thermal conductivity characteristics. </LI> </UL> </P>
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Lee, Ji Hyun,Jung, Aeran,Park, Han Na,Lee, Changhee,Mandava, Suresh,Lim, Sung-jun,Lim, Byoung-bok,Park, Sung-Kwan,Lee, Jongkook,Kang, Hoil Elsevier 2018 Forensic science international Vol.291 No.-
<P><B>Abstract</B></P> <P>Illicit psychoactive substances have threatened public health worldwide. An active metabolite of ADB-CHMINACA and MDMB-CHMINACA was identified for the first time in a powder-type product found in an airmail package. The structure of compound 1 was elucidated by a combination of gas chromatography-mass spectrometry (GC–MS), liquid chromatography-high resolution mass spectrometry (LC-HRMS), infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. Compound 1 was proven to be an analogue of MDMB-CHMINACA, an indazole-based synthetic cannabinoid. The methyl ester group in MDMB-CHMINACA was replaced with a carboxylic acid group in compound 1. Compound 1 was determined as 2-[1-(cyclohexylmethyl)-1<I>H</I>-indazole-3-carboxamido]-3,3-dimethylbutanoic acid and named as DMBA-CHMINACA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new indazole-3-carboxamide class synthetic cannabinoid was identified. </LI> <LI> Compound 1 was named as DMBA-CHMINACA according to the EMCDDA guideline. </LI> <LI> DMBA-CHMINACA is a hydrolysed form of MDMB-CHMINACA. </LI> <LI> DMBA-CHMINACA is a potential CB1 and CB2 agonist. </LI> <LI> DMBA-CHMINACA can work as a synthetic precursor of several synthetic cannabinoids. </LI> </UL> </P>
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Lee, Changhee,Yoon, Hachung,Park, Choi-Kyu The Korean Society of Veterinary Science 2007 大韓獸醫學會誌 Vol.47 No.4
The risk of an outbreak of classical swine fever (CSF) was evaluated in relation to the vaccination and seroprevalence of antibodies. Blood samples were collected from 60 piggeries throughout Korea and information regarding CSF vaccination habits was also obtained via in-person interviews with pig farmers. The results of the survey indicated that 51 out of 60 farms were regularly performing CSF vaccinations in reproductive herds. Farmers preferred to vaccinate their reproductive pigs before weaning (41 farms) than on (9 farms) or after weaning (1 farm). In growing herds, however, double vaccinations as recommended were implemented for only 40 farms (66.7%) and vaccine schedules were identified as being frequently ignored. Moreover, many farms (18/40) were found to vaccinate earlier or later than the recommended time. According to antibody seroprevalence levels, only 36 farms (60%) were considered to be safe regarding potential risk for a CSF outbreak. Among the remaining pig farms, 6 were at low-risk (10%), 12 were at medium-risk (20%), and another 6 were at high-risk (10%). Antibody levels were found to be consistent with vaccination status obtained from personal interview surveys. Our findings demonstrate the importance of vaccinations regarding the prevention of a CSF outbreak, suggesting that vaccinations must be promoted toward pig raisers and practitioners.
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