• Journal of Welding and Joining
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• 제27권6호
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• pp.17-24
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• 2009

The Friction Stir Welding(FSW) has mainly been used for making butt joints in Al alloys. Development of Friction Stir Lap Welding(FSLW) would expand the number of applications. Microstructure of FSLW in A5052-H112 alloy was investigated under varying rotation and welding speed. As the rotation speed was increased and the welding speed was decreased, a amount of heat was increased. As a result, bead interval was narrower, bead width are larger, and experimental bead interval was almost similar to theoretical bead interval. Typical microstructures of FSLW A5052-H112 alloy consist of three zones, including Stir Zone(SZ), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). As a amount of heat was increased, average grain size was larger in three zones. Nevertheless, the aspect ratio was almost fixed for FSLW conditions. The misorientation of SZ, HAZ and TMAZ was examined. A large number of low angle grain boundaries, which were formed by severe plastic deformation, were showed in TMAZ as comparison with SZ and HAZ. Microhardness distribution was high in order of BM, SZ, TMAZ, and HAZ. The Micro-hardness distribution in HAZ, TMAZ of upper plate were lager than lower plate. Relationship between average grain size and microhardness was almost corresponded to Hall-Petch equation.

• 대한기계학회논문집A
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• 제33권10호
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• pp.1087-1090
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• 2009

A unique process was developed to improve the mechanical properties of a circular tube. In this proposed process, a large amount of strain is applied to the wall of tube, leading to grain refinement in the material. In order to investigate characteristics of microstructural evolution such as the distribution of grain size and misorientation angle during the process, an EBSD OIM analysis was carried out. The analysis confirms that the proposed process can very effectively produce a circular tube with ultrafine-grains.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1750-1755
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• 2006

Nonoptimal placement of short-channel-length TFTs in large-grained polycrystalline Si films with a periodic microstructure, as for instance obtained via 2-shot SLS, can potentially lead to degradation in the overall uniformity of the resultant devices. In this paper, we explain and demonstrate that by simply introducing a well-defined misorientation between the devices and the periodic microstructure, it is possible to significantly reduce (and potentially entirely eliminate) the device nonuniformity problem that can arise from such a cause.

• 소성∙가공
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• 제12권4호
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• pp.376-381
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• 2003

Microstructural evolution and dry sliding wear behavior of ultra-fine grained 5052 Al alloy obtained by an accumulative roll-bonding process have been investigated. After 7 ARB cycles, ultra-fine grains with a large misorientation between neighboring grains were obtained. The grain size was about 0.2 $\mu$m. The hardness, tensile and yield strengths of the ultra-fine grained alloy increased as the amount of accumulated strain increased with the ARB cycles. Sliding wear tests of the ultra-fine grained 5052 Al alloy were conducted at room temperature. Wear rate of the ultra-fine grained alloy increased in spite of the increase of hardness. Surface of the worn specimens were examined with SEM to investigate wear mechanism of the ultra-fine grained alloy.

• 암석학회지
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• 제3권1호
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• pp.20-33
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• 1994

Some of the seven types of subgrain boundaries (Means and Ree, 1988) in octachloropropane samples show distinctive deformation patterns during their development. Type II subgrain boundaries migrate to accommodate the deformation difference between adjacent grains. The formation of Type III requires a rigid-body roation of grains to reduce misorientation of adjacent grains. Type I, IV, V and VI develop either in static or dynamic condition. Type VII form only in static environments after deformation. Ribbon grains can develop via Type III or Type IV process. The orientation pattern and density of subgrain boundaries are more or less stable through a post-deformation heating. Subgrain boundary orientations are symmetric with respect to the grain-shape foliation in pure shear. In simple shear, their maximum inclines toward the direction of shear.

• Progress in Superconductivity
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• 제5권1호
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• pp.45-49
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• 2003

We have designed and fabricated the single-layer high $T_{c}$ SQUID magnetometer consisting of a directly coupled grain boundary junction SQUID with an inductance of 100 pH and 16 nested parallel pickup coils with the outermost dimension of 8.8 mm ${\times}$ 8.8 mm. The magnetometer was formed from a YBCO thin film deposited on an STO(100) bicrystal substrate with a misorientation angle of $30^{\circ}$. The SQUID magnetometer was further improved by optimizing the multi-loop pickup coil design for use in unshielded environments. Typical characteristics of the dc SQUID magnetometer had a modulation voltage of 40 $\mu\textrm{V}$ and a white noise of $30fT/Hz^{1}$2/. The SQUID magnetometer exhibited a 1/f noise level at 10 Hz reduced by a factor of about 3 compared with that of the conventional solid type pickup coil magnetometers and a very stable flux locked loop operation in magnetically disturbed environments.s.

• 한국분말재료학회지
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• 제3권4호
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• pp.271-278
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• 1996

In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al-Mg-X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 $\mu$m were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively large particles occasionally at grain boundaries. The ultimate tensile strengths of Al-Mg-X alloys were found to decrease rather remarkably at 150 $^{\circ}C$ without the gain of the ductility at 150 $^{\circ}C$, which may result from segregation of $\beta$ ($Al_{3}Mg_{2}$) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed upon alloy systems. The ductility at 530 $^{\circ}C$ was found to be ~100%, suggesting that grain boundary sliding did not contribute to ductiliy despite he grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al-Mg-X alloys.

• 한국분말재료학회지
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• 제27권1호
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• pp.1-7
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• 2020

In this research, a new medium-entropy alloy with an equiatomic composition of FeCuNi was designed using a phase diagram (CALPHAD) technique. The FeCuNi MEA was produced from pure iron, copper, and nickel powders through mechanical alloying. The alloy powders were consolidated via a high-pressure torsion process to obtain a rigid bulk specimen. Subsequently, annealing treatment at different conditions was conducted on the four turn HPT-processed specimen. The microstructural analysis indicates that an ultrafine-grained microstructure is achieved after post-HPT annealing, and microstructural evolutions at various stages of processing were consistent with the thermodynamic calculations. The results indicate that the post-HPT-annealed microstructure consists of a dual-phase structure with two FCC phases: one rich in Cu and the other rich in Fe and Ni. The kernel average misorientation value decreases with the increase in the annealing time and temperature, indicating the recovery of HPT-induced dislocations.

• 한국표면공학회지
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• 제36권2호
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• pp.135-140
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• 2003

The difference in lattice parameter and thermal expansion coefficient between GaN and Si which results in many defects into the grown GaN is larger than that between GaN and sapphire. In order to obtain high quality GaN films on Si substrate, it is essential to understand growth characteristics of GaN. In this study, GaN layers were grown on Si(111) substrates by MOCVD at three different GaN growth temperatures ($900^{\circ}C$, $1,000^{\circ}C$ and $1,100^{\circ}C$), using AlN and LT-GaN buffer layers. Using TEM, we carried out the comparative investigation of growth characteristics of GaN by characterizing lattice coherency, crystallinity, orientation relationship and defects formed (transition region, stacking fault, dislocation, etc). The localized region with high defect density was formed due to the lattice mismatch between AlN buffer layer and GaN. As the growth temperature of GaN increases, the defect density and surface roughness of GaN are decreased. In the case of GaN grown at $1,100^{\circ}$, growth thickness is decreased, and columns with out-plane misorientation are formed.

• 한국재료학회지
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• 제27권11호
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• pp.636-642
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• 2017

In the present study the microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes was characterized and identified based on various microstructure analysis methods including optical and scanning electron microscopy, and electron backscatter diffraction(EBSD). Although low-carbon steels are usually composed of ${\alpha}-ferrite$ and cementite($Fe_3C$) phases, they can have complex microstructures consisting of ferrites with different size, morphology, and dislocation density, and secondary phases dependent on rolling and accelerated cooling conditions. The microstructure of low-carbon steels investigated in this study was basically classified into polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite based on the inverse pole figure, image quality, grain boundary, kernel average misorientation(KAM), and grain orientation spread(GOS) maps, obtained from EBSD analysis. From these results, it can be said that the EBSD analysis provides a valuable tool to identify and quantify the complex microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes.