• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.888-892
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• 1992

The chemically induced grain-boundary migration has been studied in MgAl2O4 spinel under ZnO atmosphere. MgAl2O4 compacts been prepared by sintering powder mixture of Al2O3 and MgO at 1$600^{\circ}C$ for 60 h in air. The sintered MgAl2O4 has been heat-treated at 150$0^{\circ}C$ in a ZnO atmosphere. During the heat-treatment grain boundaries have become curved or faceted, and the total area of grain boundaries have increased. In the migrated region, the ZnO content is higher by 6 wt% than that in other regions, indicating that the migration was induced by addition of ZnO. In some shrinking grains, the faceted planes of different grain boundaries for the same grain are parallel to each other. This result provide an experimental support for the coherency strain energy in diffusion layer of the shrinking grain as being the major driving force. Calculated coherency strain energy of MgAl2O4 shows the maximum at {111} planes and the minimum at {100} planes. Although the minimum surface energy is at {111} planes, the faceted moving boundaries are expected to be {100} planes because of lowest driving force for the grain-boundary migration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.3
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• pp.197-202
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• 2008

In this paper, we proposed an analytical model for TFT which has series of the polycrystalline structures. An average speed is defined as carrier speed by the electric field. The effective square is suggested as the area of grain without depletion for the changed grain size. First, physical parameters such as grain size, channel lenght and trap density, have been changed to prove the validity of the average speed model and the value of the effective square has been estimated through drain-source current.

• Restorative Dentistry and Endodontics
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• v.4 no.1
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• pp.7-9
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• 1978

Brass specimen, copper based alloy was prepared in cubic form about $1cm{\times}1cm{\times}1cm$ in volume. The specimens were mechanically compressed in one direction until the dimension distorted to 20%, 40%, 60% and 80% in length. The compressed specimens with 80% distorted in length were then heat treated in $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$ for 30 minutes. Microscopic examination was made on both compressed and heat treated specimens. The results obtained from the study were as follows: 1. Grain boundary and twin phenomenon was clearly seen in 0% and 20% compressed cases. Slip bands was appeared in 40% cases and distributed equally as well as twin. 2. The first evidence of slip bands was observed in 20% and the bands grew thicker and denser as the compression increased. 3. The density of the bands were reduced after annealing in $200^{\circ}C$ and completely disappeared at $300^{\circ}C$ cases. 4. Recrystallization was noticed unevenly in $300^{\circ}C$ cases and the evidence of twin was observed in these crystallized area. 5. In $400^{\circ}C$ cases the grain boundary was evenly found and the twin phenomenon was clearly observed. Grain boundary and twin was noticeably formed in size according to the annealing temperature increased.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.4
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• pp.197-204
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• 2003

Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 mm cell size, whereas 1:1.45 in 4 mm cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171.1 MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 mm cell size. And in 4mm cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores, It is thought to be main reason for lower flexural strength of 1.0 wt%C core.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.123-126
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• 2003

A high strength aluminum alloy bolt (A7050, T7 temper treatment) has been developed by the authors. The bolt has a small grain size in the whole area of the bolt because of the large equivalent strain followed by thermo-mechanical treatment. As the bolt made of A 7050 has a risk of stress corrosion cracking, each grain should be strengthened the grain inside than the grain boundary in order to improve the stress corrosion cracking resistance. It has been confirmed that the nano-indentation hardness at each grain inside increased with the increasing equivalent strain by thermo-mechanical treatment processing.

• Journal of Ceramic Processing Research
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• v.20 no.1
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• pp.59-62
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• 2019

Y2O3-MgO nanocomposites are promising materials for hypersonic infrared windows and domes due to their excellent midIR transmittance and mechanical properties. In this work, influence of SPS heating rate on the microstructure, IR transmittance, and mechanical properties of Y2O3-MgO nanocomposites was investigated. It was found that the average grain size decreases with a decreasing heating rate, which can be attributed to high defect concentration by rapid heating and deformation during densification. Also, the residual porosity decreases with a decreasing heating rate, which is ascribed to the enhancement of grain boundary diffusion by a large grain-boundary area (a small grain size). Consequently, high transmittance and hardness were attained by the low heating rate. On the other hand, the mechanical strength showed little difference with the heating rate change, which is somewhat different from the general knowledge on ceramics and will be discussed in this letter.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.329-329
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• 2016

Large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain numerous grain boundaries that can greatly degrade their performance and produce inhomogeneous properties. A better grain boundary engineering in CVD graphene is essential to realize the full potential of graphene in large-scale applications. Here, we report a defect-selective atomic layer deposition (ALD) for stitching grain boundaries of CVD graphene with ZnO so as to increase the connectivity between grains. In the present ALD process, ZnO with hexagonal wurtzite structure was selectively grown mainly on the defect-rich grain boundaries to produce ZnO-stitched CVD graphene with well-connected grains. For the CVD graphene film after ZnO stitching, the inter-grain mobility is notably improved with only a little change in free carrier density. We also demonstrate how ZnO-stitched CVD graphene can be successfully integrated into wafer-scale arrays of top-gated field effect transistors on 4-inch Si and polymer substrates, revealing remarkable device-to-device uniformity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.202-205
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• 1997

We investigated grain boundary effect for terrestrial applications of solar cell\ulcorner with low cost, large area, and high efficiency. Grain boundaries are known as potential barriers and recombination centers for the photo-generated charge carriers, which make it difficult to achieve a high efficiency cell. To reduce these effects of grain boundaries, we investigated various influencing factors such as thermal treatments, various grid patterns, selective wet etchings for grain boundaries, buried contact metallizations along grain boundaries, and use of metallic thin films. From the various grid patterns we learned that the series resistance of solar cell reduced open circuit voltage and consequently decreased the cell efficiency. This paper describes the effect of various grid patterns and the employment of metallic thin films for a top electrode.

• Corrosion Science and Technology
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• v.13 no.3
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• pp.87-94
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• 2014

Recently, the application of bending products has been increased since the industries such as automobile, aerospace, ships, and plants greatly need the usage of pipes. For facility fabrication, bending process is one of key technologies for pipings. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. Because of local heating and compressive strain, detrimental phases may be precipitated and microstructural change can be induced. This work focused on the effect of induction heat bending process on the properties of ASME SA312 TP316 stainless steel. Evaluation was done on the base metal and the bended areas before and after heat treatment. Microstructure analysis, intergranular corrosion test including Huey test, double loop electropotentiokinetic reactivation test, oxalic acid etch test, and anodic polarization test were performed. On the base of microstructural analysis, grain boundaries in bended extrados area were zagged by bending process, but there were no precipitates in grain and grain boundary and the intergranular corrosion rate was similar to that of base metal. However, pitting potentials of bended area were lower than that of the base metal and zagged boundaries was one of the pitting initiation sites. By re-annealing treatment, grain boundary was recovered and pitting potential was similar to that of the base metal.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.4
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• pp.25-33
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• 2001

Sn-3.5Ag-xBi alloys with five different levels of Bi (0, 2.5, 4.8, 7.5, 10 wt%) were prepared for evaluating creep properties. Cast alloys were roiled and heat treated to provide stable microstructures during the subsequent creep tests, which were conducted under constant load using dog-bone specimens. For the Bi containing alloys, creep strength showed the maximum around 2.5 wt%Bi and tended to decrease with increasing Bi content. The stress exponent of the alloy was around 4, suggesting typical dislocation creep, but the exponent was 2 for the 10 wt%Bi alloy, suggesting creep assisted by grain boundary Sliding. For the Bi containing alloys, the brittle fracture mode appeared showing small amount of reduction of area, while the ductile fracture mode was true for the Bi free alloy. Microstructural examination of ruptured specimens showed cavitations on grain boundaries normal to the load axis, and a significant of grain boundary sliding for the Bi containing alloys.