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An Evaluation of Thermal Fatigue Cracking and Chemical Reaction in Die Casting Mould
Youn, Kuk Tae,Rhyim, Young Mok,Lee, Jong Hoon,Lee, Chan Gyu,Jung, Yun Chul Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.345-346 No.-
<P>It is well known that the main failure mechanisms in die-casting mould are heat checking due to thermal fatigue and melt-out caused by chemical reaction between die and molten alloys. Thermal fatigue tests were carried out using the thermal cycle simulator to establish the proper method to estimate the thermal fatigue resistance of hot die steel. In this study, the thermal shock tester consisted of induction heating and water spray cooling unit was constructed to evaluate thermal crack propagation resistance and the sum of crack length per unit specimen length, Lm is proposed as the index representing the susceptibility to crack initiation and propagation. Also, new concept of measurement for the melt-out behavior was suggested. AISI H13 hot work tool steel was solution treated and tempered at various temperatures, to control the hardness and toughness that have effect on the behavior of thermal crack propagation. The result of thermal fatigue test showed that there is optimum value of hardness and impact energy to maximize the thermal crack propagation resistance. The influence of nitriding on melt-out resistance was also investigated. The dissolution rate due to melt-out phenomenon tended to be smaller for thicker compound layer. Furthermore, the resistance to melt-out was affected by the compound layer thickness rather than that of diffusion layer. The results of the both tests properly reflect the effect of materials properties on failure modes of die-casting mould and it means those test methods are suitable to evaluate the durability of hot work tool steel for die-casting.</P>
천소영,임영목,김두현,이재호,Chun, So-Young,Rhyim, Young-Mok,Kim, Doo-Hyun,Lee, Jae-Ho 한국마이크로전자및패키징학회 2010 마이크로전자 및 패키징학회지 Vol.17 No.1
다공성 탄소전극기지 위의 무전해 니켈도금에 관한 연구를 하였다. 다공성 탄소전극기지로는 다공도가 20 ${\mu}m$ 이상인 것과 16~20 ${\mu}m$ 인 것을 사용하였다. 소수성인 탄소 표면은 $60^{\circ}C$ 이상의 암모니아 용액에 침적함으로써 그 표면 성질이 친수성으로 변화 되었고, 40분 이상 침적 시 접촉각이 $20^{\circ}$ 이하까지 측정 되었다. 도금욕의 pH가 증가됨에 따라 탄소기지 위에 도금된 니켈 도금층의 인의 석출량은 감소하였으며 니켈 도금층이 결정질 구조를 갖는 현상이 관찰되었다. 도금층의 두께는 pH가 증가함에 따라 증가하였다. 활성화 처리를 위한 $PdCl_2$의 농도에 따른 도금층의 두께 변화는 없었으나, 도금에 필요한 $PdCl_2$의 최소농도는 5 ppm 이상인 것으로 나타났다. Electroless nickel plating on porous carbon substrate was investigated. The pore sizes of carbon substrates were 16-20 ${\mu}m$ and over 20 ${\mu}m$. The carbon surface was changed from hydrophobic to hydrophilic after immersing the substrate in an ammonia solution for 40 min at $60^{\circ}C$. The contact angle of water was decreased from $85^{\circ}$ to less than $20^{\circ}$ after ammonia pretreatment. The content of phosphorous in nickel deposit was decreased with increasing pH and then deposits became crystallized. The thickness of nickel deposit was increased with increasing pH. The minimum concentration of $PdCl_2$ for the electroless nickel plating was 5 ppm and the thickness of nickel was not significantly affected by the concentration of $PdCl_2$.
금속 미세조직의 3차원 이미지 관찰을 위한 순차적 박리 및 재구성 기술
김수현 ( Su-hyeon Kim ),임영목 ( Young Mok Rhyim ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9
Experimental techniques for serial sectioning and reconstruction were investigated in the three-dimensional imaging of microstructures in metallic materials. Mechanical polishing equipped with a light optical microscope and a digital image processor was used for the serial sectioning and reconstruction. Different processing conditions were investigated for three different alloys: Al-Si alloy, Al-SiC composite, and AZ31 magnesium alloy. Proper selection of polishing cloths and polishing abrasives was pre-requisite for obtaining good slice images. The thicknesses of the slices were precisely controlled for each alloy by changing the mechanical polishing and chemical etching conditions. Two-step polishing was a very effective method for serial sectioning of multi-phase alloys with a soft matrix and hard particles such as Al-SiC composites. Image filtering with a delineate and median filter was very useful for successful image segmentation of multi-phase alloys.(Received October 8, 2015; Accepted January 23, 2016)
Preparation and Characterization of CdSe Nanoparticles Prepared by Using Ultrasonic Irradiation
Sung, Myoung Seok,Lee, Yoon Bok,Kim, Young Seok,Rhyim, Young Mok,Kim, Jin Chun,Kim, In Bae,Kim, Yang Do Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.336 No.-
<P>CdSe nanoparticles with average particles size of ~ 3.4 nm were successfully prepared by the sonochemical reduction of a mixed solution of CdCl2, Na2SeSO3 and CH2CH2OH)2NH at room temperature. CdSe nanoparticles characterized by TEM, XPS and XRD analysis revealed the formation of high purity cubic phase CdSe nanoparticles with lattice constant of a=6.415Å. CdSe nanoparticles showed relatively large range of particle size distribution from 20 to 50 nm as the sonication time increased. UV-Vis absorption spectra showed a red-shift in the wavelength region of 545-590 nm as increasing sonication time due to the gradual growth of CdSe nanoparticles in the solution. This paper will mainly present the effects of ultrasonic irradiation on the formation and properties of CdSe nanoparticles.</P>
전제춘,이종수,임영목,정희돈 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.11
The crack closure phenomenon is important in the aspect of effecitve driving force for crack growth. Therefore, the precise measurement of crack closure load is an essential prerequisite for the determination of the effective driving force. In this study, the acoustic emission(AE) technique was employed as one of crack closure measurement methods and the results were compared with those of crack opening displacement method(CD), back face strain gage method(BFS) and surface strain gage method. Results have shown that the intrinsic fatigue Life curve(da/dN vs. ΔK_(eff)) obtained by use of the AE technique vvas best fit with the curve of high stress ratio (R=0.8) test, which implied that the AE technique could be considered as a reliable crack closure measurement method.
비수용성 매질로부터 Ni(OH)<sub>2</sub> 반응슬러리의 환원반응에 의한 니켈 분말의 제조
최은영,이윤복,윤석영,김광호,김진천,임영목,김형국,김양도,Choi Eun Young,Lee Yoon Bok,Yoon Suk Young,Kim Kwang Ho,Kim Jin Chun,Rhyim Young Mok,Kim Hyong Kuk,Kim Yang Do 한국재료학회 2005 한국재료학회지 Vol.15 No.5
Nickel Powders were synthesized by the reduction of $Ni(OH)_2$ reactant slurries from nonaqueous media, and the morphological characteristics of nickel powders with the addition of NaOH, the composition of mixed solvents, reaction temperature and reaction time were investigated. The NaOH addition changed the structure of agglomeration in the submicron range. As the volume ratio of TEA to DEA increased, the powders slightly suppressed the agglomeration between particles and their size increased. The reaction temperature on size and shape of nickel powders was significant. As reaction time was shortened from 40 min to 0.3 min at $220^{\circ}C$, size distribution of nickel powders was transferred to a narrow size distribution owing to the presence of smaller particles with below $1.0\;{\mu}m$.
Synthesis of Hollow Sphere CdSe from CdCl<sub>2</sub> Aqueous Solution Containing Ethylenediamine
Choi, Moon Hee,Lee, Yoon Bok,Kim, In Bae,Kim, Young Seok,Rhyim, Young Mok,Kim, Jin Chun,Kim, Yang Do Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.336 No.-
<P>Cadmium selenide (CdSe) of hollow sphere with 30-50nm in diameter have been prepared form the mixed solution of cadmium chloride (CdCl2), sodium selenosulfate(Na2SeSO3) and ethylenediamine (H2NCH2CH2NH2) at room temperature. The hollow sphere of CdSe was characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The molar ratio of EDA to Cd2+ ions in this system was important factor on controlled synthesis in the self-encapsulated morphology. Based on the observation on morphological difference with molar ratio of EDA to Cd2+ ion, the possible mechanism for the formation of CdSe hollow sphere was discussed.</P>
Preparation and Characterization of CdSe Synthesized from Non-Aqueous Media
Kim, Shin Ho,Lee, Yoon Bok,Cho, Seung Chan,Rhyim, Young Mok,Kim, Jin Chun,Kim, Young Seok,Kim, In Bae,Kim, Yang Do Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.336 No.-
<P>Cadmium selenide (CdSe) have been prepared by the reduction of mixed solution of cadmium chloride (CdCl2), sodium selenosulfate (Na2SeSO3) and diethanolamine ((CH2CH2OH)2NH) at temperatures of 80-200°C under Ar atmosphere. Characteristics of CdSe nanoparticles were analyzed using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) and UV-Vis absorption spectra. CdSe samples prepared at relatively low temperature of below 100°C showed cubic structure while samples synthesized at temperature above 100°C showed hexagonal phase. The increased reaction temperature caused the particle size increase as well as the agglomeration of particles to form a hollow sphere. UV-Vis absorption spectra also showed a red-shift as increasing reaction temperatures due to the gradual growth of CdSe nanoparticles in the solution. The relatively sharp absorption band from samples synthesized at 80 and 100°C can be attributed to homogeneous particle size distribution compared with those of prepared at elevated temperatures. This paper will mainly discuss the phase stability of CdSe nanoparticles as well as the hollow sphere formation.</P>