Addendum < Session : Light Metals and Alloys > : A MODEL ON THE TRANSITION OF CREEP BEHAVIORS OF BINARY ALUMINUM ALLOYS

Sun Ig Hong 대한금속재료학회 ( 구 대한금속학회 ) 1995 Advanced Material and Processing Vol.3 No.-

Thermally activated deformation and the rate controlling mechanism in CoCrFeMnNi high entropy alloy

Hong, Sun Ig,Moon, Jongun,Hong, Soon Ku,Kim, Hyoung Seop Elsevier 2017 Materials science & engineering. properties, micro Vol.682 No.-

<P><B>Abstract</B></P> <P>The nature of obstacles to dislocation motion in CoCrFeMnNi alloy was analyzed using the thermally activated deformation analyses at low temperatures. The strong temperature dependence of yield stress and small activation volume in CoCrFeMnNi favor the dislocation glide over the obstacles with high friction stress. The activation volume of CoCrFeMnNi alloy (10–100 b<SUP>3</SUP>) in this study is much smaller than those of conventional FCC metals (10<SUP>2</SUP>~10<SUP>3</SUP> b<SUP>3</SUP>), but close to those observed in BCC metals (8–100 b<SUP>3</SUP>) and HCP metals (5–100 b<SUP>3</SUP>). The increase of the activation volume with strain supports overcoming the nanoscale inhomogeneity such as co-clusters and/or short range orders as the rate controlling mechanism. The transition of dislocation structure from planar array to cell structure at 20% strain in CoCrFeMnNi reported in the literature can be attributed to the prevalent shearing of nanoscale inhomogeneity with strain.</P>

Influence of Dynamic Solute - Dislocation Interaction on High Temperature Ductility of Al - Mg Alloys

Hong, Sun Ig 대한금속재료학회(대한금속학회) 2000 METALS AND MATERIALS International Vol.6 No.2

High temperature ductility of Al-Mg alloys was examined as a function of stress and strain rate. T'he ductility was observed to depend strongly on the stress and/or the strain rate in the temperature range between 500 and 800 K. The elongation maximum experimentally observed at about 10 ㎫ in Al-0.94 Mg alloy at 643 K is due to the low stress exponent, which spreads the deformation out over the whole gauge length, resulting in an elongation maximum. This study also predicts the elongation minimum at about 55 ㎫ at 533 K. The decrease in elongation observed in the high stress region at 533 K is due to the high stress exponent, which concentrates the deformation in the necked region, resulting in a decrease in elongation. In this study, a solute strengthening map was constructed using the concept of dynamic solute-dislocation interaction. In region I of the map, the deformation is characterized by high ductility and random distribution of dislocations, while in region II, the deformation is characterized by low ductility and dislocation clusters. This map can be used to predict the deformation behavior of many alloys. The predicted strain rate range of high ductility associated with high strain rate sensitivity due to the solute-dislocation interaction coincides with the range of high temperature superplasticity of Al-Mg alloys, which suggests that the dynamic solutedislocation interaction contributes to this superplasticity.

Nanostructural analysis of trabecular bone

Hong, Sun Ig,Hong, Soon Ku,Kohn, David H. Springer-Verlag 2009 Journal of materials science, Materials in medicin Vol.20 No.7

등통로각압축공정을 이용하여 제작된 Cu-15wt.%Ag 미세복합재료의 미세구조 및 기계적, 전기적 특성

홍순익 ( Sun Ig Hong ),조규진 ( Kyu Jin Cho ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.2

Equal channel angular pressing (ECAP) with intermediate heat treatment was employed to optimize the strength of Cu-15 wt.%Ag. Changes in microstructure, electrical properties and mechanical properties were studied as a function of pressing methods and heat treatment. ECAPed Cu-15wt.%Ag exhibited ultrafine-grained microstructures with the shape and distribution of Ag-rich lamellae dependent on the processing routes. For route A in which the sample was pressed without rotation between each pass, the initial dendrites of Ag-rich phase were elongated along the shear direction and developed into elongated filaments. For route C in which the sample was rotated by 180 degree after each pass, the morphology of initial dendrites of Ag-rich phase was not much modified and the networked structure remained even after 8 passes of ECAP. For route Bc in which the sample was rotated by 90 degree after each pass, the initial dendrites became finer by fragmentation with no pronounced change of the shape and distribution of Ag-rich lamellae. The strength of Cu-15wt.%Ag ECAPed using route Bc was found to be greater than those ECAPed using route A, suggesting that the substructural strengthening is more effective in strengthening than the interface strengthening.

초청논문 : 고용체합금에서 슬립거동에 미치는 합금원소의 영향

홍순익 ( Sun Ig Hong ) 대한금속재료학회 ( 구 대한금속학회 ) 1994 재료강도 심포지엄 Vol.- No.-

가공공정으로 제조된 Cu-Ag 합금의 미세구조 및 기계적 특성

홍순익,송재숙,임문수 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1

The microstructural and mechanical stability of Cu-6 wt.%Ag alloys obtained by cold rolling combined with intermediate heat treatments have been investigated and compared with those of Cu-24wt.%Ag. The stress-strain responses and fracture behavior of Cu-6 wt.%Ag alloys were examined and correlated with the microstructual change caused by thermo-mechanical treatments. The linear white markings are thought to be deformation bands stabilized by silver atoms, not silver filaments as eutectic Cu-Ag alloy. The highly deformed microstructure stabilized by silver filament is unstable at temperatures above 300℃ because of the increase of the diffusivity of silver atoms. The strength of Cu-6 wt.%Ag alloys were found to be decreased remarkably if they were heat-treated above 300℃ for 1hr. The fracture surfaces of Cu-6 wt.%Ag alloys showed topical ductile type fracture. The electrical conductivity did not change appreciably up to the aging temperature of 200℃ and increased rapidly at temperatures above 300℃. The increase of the conductivity and the decrease of the strength can be associated with the coarsening and spheroidization of highly deformed linear band structure. The strengthening mechanism and microstructural stability were discussed based on the microstructural analyses.

Cu-Nb 미세복합재료의 미세구조의 안정성 및 강화기구 : (2) 강화기구 (2) Strengthening Mechanism

홍순익,안장호 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.5

In this study, the deformation and fracture behavior of the Cu-Nb microcomposites fabricated by the bundling and drawing process was investigated. The yield strength of a Cu-20% Nb microcomposite was predicted by modifying the model of Verhoeven et al. It was assumed that the substructural strengthening in pure Cu and Nb phase fully contribute to the yield strength of Cu-Nb microcompoaite, σ_(Cu-Nb), at low draw strains (η $lt; 5.5). At high drawing strains (η $gt; 5.5) where the microstructural scale of the Cu matrix is limited by Nb filaments, the contribution of the partial grain boundaries (connecting the edge of Nb filaments) to the strength was assumed to be proportional to (λ/W_(Nb))^½ The good agreement between the yield stress predicted in this study and the experimental data at drawing strains between 6 and 9.5 supports the suggestion of the present study that the effectiveness of substructure strengthening of Cu and Nb in heavily deformed Cu-Nb microcomposites is much lower than that expected from the yield strength of heavily deformed Cu and Nb. The yield stress of the Cu-Nb microcomposite fabricated by the bundling and drawing process was found to be in good agreement with the predicted yield stress of the present model. At drawing strains above 10, Nb filaments reached a thickness of approximately 10 ㎚ and there after further working resulted in random rupture of the filaments rather than continued plastic deformation and thinning, which may result in the slower increase of the strength than the predicted values with drawing strain.

Criteria for predicting twin-induced plasticity in solid solution copper alloys

Elsevier 2018 Materials science & engineering. properties, micro Vol.711 No.-

<P><B>Abstract</B></P> <P>The deformation-mode transition model was extended to predict wavy to planar-slip and subsequent twin-induced plasticity (TWIP) transitions in solid solution copper alloys. In the deformation-mode map, the stacking fault energy (γ/G) vs. frictional-stress (2<I>F</I> <SUB>f</SUB>/G) curves for Cu-Al, Cu-Mn, and Cu-Zn, crossed the boundaries of wavy-slip to planar-slip and planar-slip to TWIP transitions, with an increase in the solute content. The critical solute content predicted for the transition from wavy-slip to planar-slip to TWIP, by the deformation-mode transition model, was in good agreement with observations for solid solution copper alloys. Excellent agreement between the predictions and experimental data in the literature suggested that TWIP in Cu alloys is enhanced not only by the low stacking fault energy, but also by the frictional-stress on twinning partial-dislocations.</P>

New strategy for detecting gestational diabetes mellitus in Korean

( Hong Subeen ),( Lee Seung Mi ),( Jung Young Mi ),( Lee Se Jin ),( Koo Ja Nam ),( Oh Ig Hwan ),( Kim Byoung Jae ),( Kim Sun Min ),( Park Chan-wook ),( Jun Jong Kwan ),( Park Joong Shin ) 대한산부인과학회 2018 대한산부인과학회 학술대회 Vol.104 No.-

Objective: American College of obstetricians and Gynecologists (ACOG) changed the screening strategy for early detection of gestational diabetes mellitus (GDM) or type 2 DM, which had been established by American Diabetes Association in 2017. The new strategy is the same with the strategy for detecting type 2 DM for asymptomatic adults. However there is not enough information about how the strategy is suitable for detecting GDM. We evaluated diagnostic performance of the new strategy for the detection of GDM in Korean Women. Methods: Study population included enrolled singleton nondiabetic women during 3 years from November 2014 to October 2017. Maternal fasting blood was taken and measured for laboratory parameters at 10-14weeks of gestation. GDM was diagnosed by the two step approaches, which are screening using 50g oral glucose tolerance test (OGTT) and then following 100g OGTT. The high risk population of the new strategy was defined as overweight women who have one or more of the risk factors including family history of DM, history of cardiovascular disease, GDM or polycystic ovarian syndrome, physical inactivity, dyslipidemia including triglyceride >250mg/dL or high density lipoprotein < 35mg/dL, impaired glucose metabolism and hypertension. The odds ratio of risk factors was calculated by multivariate logistic regression. Results: Among 1,077 pregnant women, 62 (5.8%) women was diagnosed for GDM and 20 (1.9%) women with GDM were managed on insulin. Prepregnancy obesity (aOR 4.41), previous GDM (aOR 5.85), impaired fasting glucose (aOR 12.93), triglyceride >250mg/dL (aOR 14.72) were remained after adjustment for confounding variables. Conclusion: Prepregnancy obesity, previous GDM, impaired fasting glucose, and high triglyceride level were independent risk factors for GDM. Pregnant women might be screened for these risk factors at the first prenatal visit and considered for the high risk population for GDM.