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Joo‑Youl Huh,Min‑Je Hwang,Seung‑Woo Shim,Tae‑Chul Kim,Jong‑Sang Kim 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6
The reactive wetting behaviors of molten Zn–Al–Mg alloys on MnO- and amorphous (a-) SiO2-covered steel sheets wereinvestigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests werecarried out at 460 °C and the variation in the contact angles (θc) of alloys containing 0.2–2.5 wt% Al and 0–3.0 wt% Mg wasmonitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the a-SiO2-coveredsteel exhibited nonreactive, nonwetting (θc > 90°) behavior. The MnO layer was rapidly removed by Al and Mg contained inthe alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreasedupon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the a-SiO2 layer were found to be sluggish, the wettabilityof Zn–Al–Mg alloys on the a-SiO2 layer improved upon increasing the Al and Mg contents. These results suggest that thewetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and SiO2,withZn–Al–Mg alloys could be most effectively improved by increasing the Mg content of the alloys.
A Generalized Thermodynamic Treatment of Phase Equilibria in Coherent Multilayers
Huh, Joo Youl 대한금속재료학회(대한금속학회) 1997 METALS AND MATERIALS International Vol.3 No.2
We present a generalized way of treating phase equilibria in coherent planar multilayers. A correct recognition of elastic stress and strain components as thermodynamic potentials or densities is crucial for the use of the criteria for intrinsic stability as well as for the applicability of the conventional method of common tangent construction and the Gibbs phase rule. It is shown that a method analogous to the conventional common tangent construction exists in thermodynamic density subspaces for which some of density variables are held constant. In a thermodynamic density subspace with ms density variables fixed, a common tangent construction can be made between the extremized free energies for systems of (m_s+1)-phase coexistence in order to satisfy the thermodynamic equilibrium conditions of systems with more than ms+l coexisting phases. This method is applied to a coherent binary system configured as plane-parallel plates to demonstrate that equilibrium states with more than two coexisting phases cannot be thermodynamically stable in the binary multilayer system under certain mechanical loading conditions.
Huh, Joo-Youl,Han, Sang-Uk,Park, Chang-Yong 대한금속재료학회 2004 METALS AND MATERIALS International Vol.10 No.2
The effect on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints, caused by adding Bi to eutectic Sn-3.5Ag solder alloy, was examined at the aging temperatures of 150℃ and 180℃. The Cu_(6)Sn_(5) layer growth was significantly enhanced, but the Cu₃Sn layer growth was slightly retarded by the addition of Bi, resulting in significant growth enhancement of the total (Cu_(6)Sn_(5)+Cu₃Sn) IMC layer with increasing Bi addition. The IMC layer growth in the Bi-containing solder joints was accompanied by the accumulation of Bi ahead of the Cu₃Sn layer that resulted in the formation of a liquid layer at the Cu_(6)Sn_(5)/solder interface. A kinetic model was developed for the planar growth of the Cu_(6)Sn_(5) and Cu₃Sn layers in the solder joints, accounting for the existence of interfacial reaction barriers. Predictions from the kinetic model showed that the experimental results could be well explained by the hypothesis that the formation of a Bi-rich liquid layer at the Cu_(6)Sn_(5)/solder interface reduces the interfacial reaction barrier at the interface.
리플로우 솔더링시 솔더/Cu 계면반응속도에 미치는 Cu- 첨가 솔더의 영향
허주열,강대웅 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1
We have investigated the effects of Cu additions to pure Sn and eutectic Sn-Pb solders on the morphology and growth kinetics of the intermetatllics (Cu_6Sn_5) and on the consumption rate of Cu substrate during isothermal reflow soldering. The consumption rate of Cu substrate could be reduced with increasing Cu content in both Sn and Sn-Pb solders up to the respective solubilities at reflow temperatures. The effect of Cu addition was more significant for the Sn solder which had a higher Cu solubility. The Cu addition also resulted in morphological changes of the intermetallic layer. With increasing Cu content, the interface between Cu_6Sn_5 layer and solder roughened for pure Sn solder whereas it flattened fur the eutectic Sn-Pb solder. When the time(t) dependence of the intermatallic layer thickness(X ̄) was modelled as X ̄ = a×t^n, the growth constant a appeared to increase with the Cu content whereas the growth exponent n decreased. It was shown that the growth kinetics of the intermetallic layer could be well interpreted by a model of grain boundary diffusion controlled growth.
High Temperature-Induced Flower Abnormalities at Bud Development in Chrysanthemum
Eun Joo Huh,Hak Ki Shin,Kwang Jin Kim,Seong Youl Choi 한국원예학회 2004 Horticulture, Environment, and Biotechnology Vol.45 No.6
The effects of high temperature (HT) on flower development were examined on chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura]. Plants exposed to HT developed two types of abnormal flowers. One formed only ray florets, and the other developed ray florets with bracts at the center of the disk. These abnormal flowers occurred when the plants were exposed to a HT of 35℃ from 14 to 27 days after the start of short day (SD). The most susceptible developmental stage was 14 to 20 days after SD. Having a 4-h HT period before nighttime induced abnormal inflorescence and delayed flowering. This result suggested that HT just before night especially from 14 to 20 days after SD is responsible for abnormal flower formation in a single type of chrysanthemum.