• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.281-284
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• 2003

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment is investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) are hot extruded to make I-shape bars at 380$^{\circ}C$, then the bars are solution treated at 480$^{\circ}C$ for 2hrs followed by artificial aging at 120$^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consists of elongated grains, however, fine equiaxed grains are mainly observed around surface. The microstructural gradient suggests that different restoration process can proceed during the hot extrusion. For B1 and B2, different grain growth behaviors are found around the surface during the post heat treatment. Rapid grain growth behavior around the surface is discussed related with the crystallographic orientation of the grain.

• 한국세라믹학회지
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• 제30권5호
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• pp.404-410
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• 1993

The characterization and sintering behavior of ZnO powders prepared by precipitation method were investigated. ZnO powders were synthesized using the aqueous solutions of ZnCl2 and NH4OH as a precipitation agent, which were crystallized in the shape of plate-like. The grain growth of ZnO(0.68${\mu}{\textrm}{m}$, 1.3${\mu}{\textrm}{m}$ and 3.4${\mu}{\textrm}{m}$) has been studied for temepratures from 100$0^{\circ}C$ to 130$0^{\circ}C$, and the rate of densification was inversely proportional to the ZnO particle size. Densification proceeded slowly by diffusion mechanisms above at 100$0^{\circ}C$. In this work, the grain growth kinetic exponent(n) was 3. The temperature dependence of ZnO grain growth was plotted, and the activation energy of grain growth was 75~85Kcal/mol.

• 한국재료학회지
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• 제16권1호
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• pp.68-74
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• 2006

2024 Al alloys were severely deformed by equal channel angular pressing(ECAP) to obtain an ultrafine grain structure. The more deformation amount increased, the more grain size decreased. Most of the grain structure were changed from elongated to equiaxed shape with increasing pass number. The morphology of S' phases was also changed from rod-type to spherical type. The grain size of 6 passed specimen was 100 to 200 nm, and the size of S' phases was about 10 nm in the microstructure. XRD measurements have revealed that the texture formed by plastic deformation disappeared in the 6 passed specimen. SP test results described that the start of crack propagation occurred at the transition zone between plastic bending and membrane stretching because of small elongation. The maximum strength of ECA pressed specimen increased 1.9 GPa to 2.9 GPa with increasing pass number.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.81-84
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• 2003

The effect of annealing condition on the texture and microstructure development in Ni tapes fabricated by cold-rolling including powder metallurgy was investigated. The Pole-figure results showed that the Ni tapes annealed at lower temperature than 50$0^{\circ}C$ were the mixture of brass deformation texture and cube texture. The specimens annealed at high temperatures had only well-developed cube texture and the FWHMs of in-plane and out-of-plane were in the range of 8-10$^{\circ}$. The degree of texture was not significantly depended on annealing temperatures. The grain morphologies of Ni tapes prepared at low temperatures showed serrated grain boundaries due to incomplete recrystallization, but the specimens prepared at high temperatures showed stabilized grain shape without serrated grain boundaries.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.209-213
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• 2000

Microstructural changes of AlOOH doped UO$_2$pellet after annealing up to 216h have been observed and they were compared with those of the standard pellet. Grain and pore size of UO$_2$pellet increased with the addition of AlOOH and its effect was still validated during annealing. Densification rate was reduced by the addition of AlOOH and it was attributed to coarsened pores with spherical shape. Grain and pore growth was stopped and density increase was the least after 144h of annealing. The variation of pore size resulting from annealing has a linear relationship with that of grain size.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.352-355
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• 2007

Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2s^{-1}$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimen is investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which contain grain size, grain shape, aspect ratio and dislocation substructure.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.70-71
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• 2006

Growth behavior and kinetics of grains in a liquid matrix has been studied by computer simulation for various physical and processing conditions. The kinetics of growing and dissolving grains were considered to follow those of single crystals in a matrix. Depending on the shape of crystals, rounded or faceted, different kinetic equations were adopted for growing grains and an identical equation for dissolving grains. Effects of such critical parameters as step free energy, temperature, and liquid volume fraction were evaluated.

• 한국군사과학기술학회지
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• 제14권6호
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• pp.1114-1120
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• 2011

Shaped Charge's penetration performance is depended on the shape of warhead and explosive, liner materials. The liner that manufactured to small homogeneous grain increase the penetration performance and decrease the deviation of penetration performance. This texture is obtained by forging process but, creating the process that remove crack and get small homogeneous grain is very hard. In this study, We success to get the homogeneous small grain texture through appling the most suitable process by DEFORM CODE analysis.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
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• pp.89-92
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• 2005

This study investigates influence of particle properties of crushed sand on the duality of concrete. The test shows that an increase of fineness modulus(FM) resulted in high slump and air contents, while compressive strength decreased due to decreased adhesion with reduction of surface area. As grain shape become rounder, the slump of concrete increased, due to reduction of internal friction, and increased air contents. The reduction of adhesion by abrasion of surface declined compressive strength during the process of manufacturing crushed sand. Increase of powder contents decreased slump and it also decreased air contents due to the effect of filling air void. In addition. using powder contents increased compressive strength, but could not find any difference of bleeding and tensile strength with particle properties.

• 분석과학
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• 제11권4호
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• pp.316-320
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• 1998

An image analysis was used for the interpretation of microstructures of ferrous metal artifacts. For the purposes, various microstructural features such as average grain size, phase area, shape factor, and composition of the inclusions, were parameterized for the information about manufacturing techniques such as casting, heating and tempering. The carbon content was determined through the evaluation of the amount of pearlite phase. As the amount of pearlite phase increased the shape factor also increased. Grain size was relatively smaller in trans-section than in cross-section. The manufacturing direction was trans-sectional because the orientation of inclusions was elongated lengthwise. All inclusions was of silicate groups and the manufacturing temperature was estimated up to $1450^{\circ}C$.