• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.167-171
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• 1995

The formation of preferred orientations in cold rolled and recrystallized Inconel 690 sheets was studied by the x-ray texture measurements and TEM observations. The increasing{220} pole intensity in the plane normal at the higher reductions was related to the{110}<112> texture component. The rolling texture of the Inconel 690 was the pure metal type. THe dislocation cells were found in the near{110}<112> oriented grains. The onset of deformation twins in the {112}<111>oriented grains. The onset of deformation twins in the {112}<111> oriented grains. The onset of deformation twins in the {112}<111> oriented grains caused the weakening of {112}<111> and the development of {552}<115> in the rolling texture. The annealing texture of the Inconel 690 sheets was dependent on the annealing temperature. The annealing texture of 750$^{\circ}C$ annealed sheets was similar to the cold rolling texture. The major preferred orientations of the 950$^{\circ}C$ annealed specimens were {112}<110> and {001}<110>. The formation of fine and closely spaced annealing twins in the specimen annealed at 1150$^{\circ}C$ led to the randomization of the annealing texture.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.274-282
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• 1998

The effect of Al addition on the fatigue properties of austenitic Fe-25Mn-Al-0.5C steels was studied. When Al was not added to the Fe-25Mn 0.5C steel, the strain induced ${\varepsilon}$ martensites, deformation twins and slip bands were formed during fatigue deformation. When 2wt% of Al was added to the steel, the deformation twins and slip bands were formed during fatigue deformation. When 5wt% of Al was added, only slip bands were formed. In low cycle fatigue test, the alloys containing 0wt% and 2wt%Al showed the cyclic hardening due to ${\varepsilon}$ martensites and deformation twins, resulting in shorter fatigue lives than the alloy containing 5wt%Al. In fatigue crack propagation test, the alloy without Al showed the highest crack propagation rate. The fracture surface of the alloy without Al was flat, whereas that of the alloy with 2% or 5%Al was rough. The ${\Delta}K_{th}$, values of the alloys with 0%, 2% and 5%Al were 16, 17.5, and $20.5MPam^{1/2}$, respectively.

• The Korean Journal of Ceramics
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• v.4 no.3
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• pp.207-212
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• 1998

By comparison of the experimental results in two systems of ZnO varistors, it's appear that Sb2O3 is the indispensable element for twining in ZnO varistors and the Zn7Sb2O12 spinel acts as the nucleus to form twins. Al2O3 is not the origin of twining in ZnO varistor, but it was found that Al2O3 could strengthen the twining and form a deformation twining by ZnAl2O4 dragging and pinning effect. The inhibition ratios of grain and nonuniformity of two systems ZnO varistors increase with the increase of Al2O3 content. The twins affect the inhibition of grain growth, the mechanism could be explained follow as: twins increase the mobility viscosity of ZrO grain and grain boundary, and drag ZrO grain and liquid grain boundary during the sintering, then the grain growth is inhibited and the microstructure becomes more uniform.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.416-422
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• 2010

The $\{10\bar{1}2\}$ twinning characteristics, such as active twin variants, volume fraction of twins with strain, twin morphology, twin texture and angle relationship between twins, were dependent on the activation mode (i.e., tension parallel to the caxis or compression perpendicular to the c-axis). The selection criterion of active twin variants was governed by the Schmid law. This activation of selected twin variants depending on the activation mode consequently caused a totally different plastic deformation behavior in two activation modes. The differences in the deformation characteristics, such as flow stress and work hardening rate, between both activation modes were explained in relation with activation stresses for slips and twinning, relative activities of twinning and slips during plastic deformation, grain refining effect by twin boundaries (Hall-Petch effect), and twinning-induced change in activities of slips.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.1057-1060
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• 2001

By comparison of the experimental results in two systems of ZnO varistors, its appear that Sb$_2$O$_3$is the indispensable element for twinning in ZnO varistors, and the Zn$_{7}$Sb$_2$O$_{12}$ spinel acts as the nucleus to form twins. A1$_2$O$_3$is not the origin of twinning in ZnO varistor, but it was found that A1$_2$O$_3$could strengthen the twinning and form a deformation twinning by ZnA$_{12}$O$_4$-dragging and pinning effect. The inhibition ratios of grain growth and nonuniformity of two systems ZnO varistors increase with the increase of A1$_2$O$_3$content. The twins affect the inhibition of grain growth, the mechanism could be explained follow as : twins increase the mobility viscosity of ZnO grain and grain boundary, and drag ZnO grain and liquid grain boundary during the sintering, then the grain growth is inhibited, and the microstructure becomes more uniform.orm.m.

• Economic and Environmental Geology
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• v.40 no.4
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• pp.461-471
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• 2007

A temperature of deformation and the state and direction of paleostress at that time when twins in calcite grains had been produced were observed, using analysis of calcite twins as indicators of paleostress history. The study was performed with the target of carbonate rocks distributed randomly small size in the southern area of south Korea. Considering the appearance of twins (thin or thick straight twins with one or two twin sets), average twin strain (1.235-7.453%), thickness ($0.77-1.94{\mu}m$) and intensity (25.26-41.99 twins/mm) from the results of calculated calcite twins, it is estimated that calcite twins were produced under temperatures lower than approximately $150-200^{\circ}C$. In the magnitudes and directions of principal strains, the maximum shortening strain axis ($e_3\leftrightarrow{\sigma}_1$) is approximately N-S direction in the GS-1 area in the southern Gyeongsang Basin as well as in the BS-1 area in the southern Yongnam Massif, whereas E-W direction in the NR-1 area in the southwestern Ogcheon Fold Belt. In case of the maximum extension strain axis ($e_1\leftrightarrow{\sigma}_3$), it is oriented in NW-SE and NE-SW directions in the GS-1 and BS-1 area, respectively, and in N-S direction in the NR-1 area. That is, it is suggested that the paleostress which produced the calcite twins may be applied at least more than two times in the study area.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.4
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• pp.277-287
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• 1994

The effect of grain size on the tensile properties and fatigue behavior of austenitic high Mn steel has been investigated. The recrystallized austenite grain size of the cold rolled high Mn steel was increased as the annealing temperature increased from $600^{\circ}C$ to $1000^{\circ}C$. Larger austenite grain size decreased the yield strength and the tensile strength, and increased the uniform elongation due to transformation of some austenite into twins or E-martensite phase during deformation. Austenite grain refinement increased the tendency to form dislocation cells, instead. The specimen annealed at $1000^{\circ}C$ with large grain size showed lower fatigue crack propagation rate in low ${\Delta}K$ region due to rougher fracture surface caused by formation of deformation twins during fatigue at the crack tip region.

• Transactions of Materials Processing
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• v.3 no.4
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• pp.392-400
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• 1994

The formation of preferred orientations in the cold rolling texture of the Inconel 690 sheets was studied by the x-ray texture measurements and TEM observations. The increasing {220} pole intensity in the plane normal at the higher reductions was related to the {110}<112> texture component. The rolling texture of the Inconel 690 was the pure metal type which could be described by {112}<111>, {123}<634> and {110}<112> orientations. The dislocation cells were found in the near {110}<112> oriented grains. The onset of deformation twins in the {112}<111> oriented grains caused the weakening of {112}<111> and the development of {552}<115> in the rolling texture.

• The Journal of Natural Sciences
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• v.7
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• pp.83-90
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• 1995

The microstructural and textural development during rolling is compared in two Hadifield's steels (high Mn steel), one having low carbon content (0.65 wt.%) and the other high carbon (1.35 wt.%).In low carbon Hadfield's steel (LCHS) mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. The deformation twins are thought to be formed by the stacking of intrinsic stacking faults. The similar development to 70-30 brass texture is observed in early deformation. However the abnormal texture is developed after 40 % deformation, which is thought to be due to the martensite phase transformation. In high carbon Hadfield's steel (HCHS) mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. The texture development is similar to that of 70-30 brass. This is consistant with no carbon segregation and no martensitic phase transformation in HCHS. In spite of the difference of substructure and texture development during rolling in two steels, the difference in stacking fault energy is measured to be small ($2 mJm^-2$). The carbon segregation is only occurred in LCHS. Thus it is thought that the carbon segregation influence the microstructure and texture development during rolling. This is related with martensite phase transformation in LCHS.

• The Journal of the Petrological Society of Korea
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• v.24 no.2
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• pp.125-139
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• 2015

Rock structural and microstructural analyses on the deformed Cheongsan granite, which is characterized by abundant feldspar megacrystals, have been carried out to understand the microstructural change during the mylonitization by ductile shear deformation. In K-feldspars, the characteristic microstructures are recognized as microkinks, microfractures, myrmekites, flame perthites, and core-and-mantle structures without the development of subgrains in outer core-zone. Microkinks are observed in both the microfractured and unmicrofractured K-feldspars and the directions of their axes are generally extended across the adjacent K-feldspar fragments bounded by microfractures. Myrmekites and flame perthites are found on the strain-localized boundaries of the microfractured K-feldspars. In plagiclases, microfractures, deformation twins and kink bands are predominant. Grain size reduction of plagioclase megacrysts also occurs by microfracturing but the core-and-mantle structures like the case of K-feldspars are uncommon in the microfractured plagioclases. The deformation twins, which overlap the igneous zoning structures, are often found in less deformed rocks. The twin lamellae in more deformed rocks generally bisect the obtuse angles of conjugate kink-band boundaries, and are microfractured or microfaulted and randomly oriented. From such characteristic microstructures, thus, it can be suggested that the micostructures during the mylonitzation of Cheongsan granite was developed as follows: production of microkinks in the K-feldspar megacrysts and of deformation twins and kink bands in the plagioclase megacrysts, and then grain-size reduction of the feldspar megacrysts through microfracturing, and then production of core-and-mantle structures (grain-size reduction of the microfractured K-feldspars through grain boundary migration), myrmekites and flame perthites in the microfractured K-feldspars.