• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.5
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• pp.237-241
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• 2009

Dislocation dipoles were formed in the early stage of deformation of Y-CSZ single crystal at high temperatures. And the dipoles were pinched off to break into dipoles loops by dislocation climb. Dislocation loop annealing was peformed in Y-CSZ single crystal to evaluate the diffusivity of cation which was the rate-controlling ion.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.20-26
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• 2009

The creep deformation behavior of AZ31 magnesium alloy was examined in the temperature range from 573 to 673K (0.62 to 0.73 Tm) under various constant stresses covering low strain rate range from $4{\times}10^{-9}\;s^{-1}$ to $2{\times}10^{-2}\;s^{-1}$. At low stress level, the stress exponent for the steady-state creep rate was ~3 and the present results were in good agreement with the prediction of Takeuchi and Argon model. At high stress level, the stress exponent was ~5 and the present results were in good agreement with the prediction of Weertman model. The transition of deformation mechanism from solute drag creep to dislocation climb creep could be explained in terms of solute-atmospherebreakaway concept.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.4
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• pp.201-208
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• 1992

An experimental study of the constitutive response of precipitation-strengthened Al-0.55wt% Zr alloy, which consists of an Al matrix precipitation-strengthened by coherent particles, ${\beta}^{\prime}(Al_3Zr)$ with $L1_2$ structure has been performed. The deformation response of the materials has been examined by stress relaxation test at 573K, 623K and 673K. It was found that there exist the threshold stress during stress relaxation and threshold stress results from the presense of ${\beta}^{\prime}(Al_3Zr)$ particles. The ratio of threshold stress and Orowan stress decreased gradually with increasing temperature. The resistance to climb-pass of particles was independent of particles size for a fixed volume fraction although the threshold for bowing and particles cutting are sensitive to the particles dimensions. The smaller particles cutted by dislocations. This behavior of dislocations in this alloy was explained in terms of the small value antiphase boundary energy. The dislocation networks wrere more extensive in spesimens subjected to stress relaxation and there were numerous areas that have a high denstiy of jogged dislocation. This experiment results indicate that the rate controlling stress relaxation process is the climb of edge dislocation over particles.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3408-3414
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• 1996

This paper investigated plane strain stress intensity factors caused by thermal impact on a center-crack strip. The crack was aligned perpendicularly to the strip boundary. The problem was analysed by determining the dislocation density function in the singular integral equations formulated by the dislocation theory. Under the abrupt temperature change along the edge, the center crack behaved as a mode I crack due to the symmetric geometry. The value of maximum stress intensity factor monotonically increased until the ratio of dimensionless crack length approached to about 0.3, followed by gradual decrease. As a result, a critical corresponding crack length was determined.

• Applied Microscopy
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• v.16 no.2
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• pp.14-24
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• 1986

The interrelation of secondary defects, intermediate S' phase and aging condition in Al-2.0 wt% Cu-1.1 wt% Mg alloy is studied by transmission electron microscope. The results obtained in this study are as follows. 1. High density of dislocation loops, helices and stacking faults are observed in this specimen with aging treatment. 2. The number of dislocation loops and the width of loop free zone (LFZ) are increased with aging time. 3. The intermediate S' phase precipitates and grows on the dislocations and secondary defects. 4. The misfit dislocations are formed around intermediate S' phase. 5. It is thought that the helices appear to be produced by the climb of screw dislocations, while the dislocation loops appear to be formed both by condensation of vacancies into collapsed discs and by interaction of helices with screw of opposite sign.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.58-62
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high n austenitic steels. After measuring the internal stress in minimum creep rate state under applied stress of 236MPa at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band widths and values of internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.332-337
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.238-251
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• 1995

Creep of metals has been explained conventionally by dislocation climb and grain boundary sliding indiffusion controlled process. The reorienations of the atoms in the grain by three dimensional crystallizing $\pi$-bondings are visualized as grain rotatins during slow deformation, fold formatin at triple point, increased crevice dspace between grains. grain boundary sliding, grain boundary micration and formation of cracks at the grain boundaries . And also the rupture time and average creep strain rate are explained by the three-dimensional crystallizing $\pi$- bondings and they can be determined by uniaxial tensile test.

• Transactions of Materials Processing
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• v.11 no.6
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• pp.529-537
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• 2002

A series of load-relaxation tests and tensile tests were conducted to study the high temperature deformation mechanism of fine duplex gamma TiAl alloy at temperatures ranging from 800 to 105$0^{\circ}C$. Results of load relaxation test showed that deformation behavior at a small imposed strain ($\varepsilon$≒0.05) was dominated by dislocation glide and dislocation climb. To investigate the deformation behavior at a large amount of strain, the processing map was constructed using a dynamic materials model. Two domains were characterized in the processing map obtained at a strain level of 0.6. One domain was found at the region of 98$0^{\circ}C$ and $10^{-3}/sec$ with a peak efficiency of 48%, which was identified as a domain of dynamic recrystallization from the microstructural observation. The order was observed at the region of 125$0^{\circ}C$ and $10^{-4}/sec$ with a peak efficiency of 64%. The strain rate sensitivity measured indicates that the material was deformed by the superplasticity in the region.

• Korean Journal of Materials Research
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• v.26 no.4
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• pp.167-172
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• 2016

The high temperature deformation behavior of $Ni_3Al$ and $Ni_3(Al,Mo)$ single crystals that were oriented near <112> was investigated at low strain rates in the temperature range above the flow stress peak temperature. Three types of behavior were found under the present experimental conditions. In the relatively high strain rate region, the strain rate dependence of the flow stress is small, and the deformation may be controlled by the dislocation glide mainly on the {001} slip plane in both crystals. At low strain rates, the octahedral glide is still active in $Ni_3Al$ above the peak temperature, but the active slip system in $Ni_3(Al,Mo)$ changes from octahedral glide to cube glide at the peak temperature. These results suggest that the deformation rate controlling mechanism of $Ni_3Al$ is viscous glide of dislocations by the <110>{111} slip, whereas that of $Ni_3(Al,Mo)$ is a recovery process of dislocation climb in the substructures formed by the <110>{001} slip. The results of TEM observation show that the characteristics of dislocation structures are uniform distribution in $Ni_3Al$ and subboundary formation in $Ni_3(Al,Mo)$. Activation energies for deformation in $Ni_3Al$ and $Ni_3(Al,Mo)$ were obtained in the low strain rate region. The values of the activation energy are 360 kJ/mol for $Ni_3Al$ and 300 kJ/mol for $Ni_3(Al,Mo)$.