• Journal of Powder Materials
• /
• v.27 no.4
• /
• pp.339-342
• /
• 2020

Since the interaction between the second-phase particle and grain boundary was theoretically explained by Zener and Smith in the late 1940s, the interaction of the second-phase particle and grain boundary on the microstructure is commonly referred to as Zener pinning. It is known as one of the main mechanisms that can retard grain growth during heat treatment of metallic and ceramic polycrystalline systems. Computer simulation techniques have been applied to the study of microstructure changes since the 1980s, and accordingly, the second-phase particle-grain boundary interaction has been simulated by various simulation techniques, and further diverse developments have been made for more realistic and accurate simulations. In this study, we explore the existing development patterns and discuss future possible development directions.

• Journal of the Korean Ceramic Society
• /
• v.38 no.10
• /
• pp.914-920
• /
• 2001

The grain orientation distribution and grain boundary characterization of $ZrB_2$-ZrC composites sintered by a SPS(Spark Plasma Sintering) method, a new sintering technique were analyzed by the EBSP technique and then their crystallographic results have been compared with those of a sintered specimen using a PLS(Pressureless Sintering) method. In the $ZrB_2$-ZrC composite manufactured by SPS, (0001) planes of $ZrB_2$ were oriented in the direction normal to the specimen surface. In the case of PLS, those of $ZrB_2$ were oriented normal to the electron beam. In both cases of PLS and SPS, ZrC grains had the randomly oriented grain structure. The grain boundary characterization showed that low angle grain boundaries in the PLS and SPS processed materials constituted about 10% and 8% of the total number of boundaries, respectively, represented the only slight difference between the proportion of low angle grain boundary. However, in the distribution of CSL(Coincident Site Lattice) boundaries, it was shown the higher proportion of CSL boundaries with $\Sigma$ 3,5,7,9, 11 in the SPS processed material.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1315_1316
• /
• 2009

ZnO는 비선형 전류전압 특성으로 인해 급작스런 과전류로부터 회로를 보호하는 바리스터로 널리 사용되고 있다. 이러한 바리스터의 전기적 특성 및 미세조직을 제어하기 위하여 다양한 첨가물을 넣은 ZnO 바리스터의 미세구조에는 대부분의 입자에 wurtzite 구조의 결정학적 극성이 바뀌는 inversion boundary (IB)가 존재한다. ZnO의 비선형 전류전압 특성이 반도성의 ZnO 입자간 계면에 형성되는 쇼트키 장벽에 기인함을 감안할 때 계면의 결정화학적 특성에 영향을 주는 IB에 대한 이해는 필수적이다. 본 연구에서 IB가 ZnO 바리스터의 성능에 미치는 영향을 규명하기 위하여 ZnO-$Bi_2O_3$에 각각 $Sb_2O_3$ 또는 $TiO_2$ 를 첨가하여 결정학적 특성이 서로 상반되는 IB를 유도하였고, 첨가량을 조절하여 모든 입자가 IB를 가지도록 하였다. 화학 에칭을 한 시편의 SEM 관찰을 통해 입자의 형상, 크기, 분포 및 IB의 결정학적 특성 등을 분석하였다. 각 시편의 바리스터 특성은 임피던스의 온도 의존성과 상온에서의 전류-전압 특성을 통해 평가하였다. 관찰된 전기적 특성들을 입내 IB의 결정학적 구조와 이로부터 결과되는 입계면의 극성의 차이를 통해 해석하고자 한다.

• Analytical Science and Technology
• /
• v.5 no.2
• /
• pp.203-211
• /
• 1992

Fracture behavior and martensite substructure of Ni-36.5at.%Al alloy were investigated with the addition of vanadium which is known as scavenging element of grain boundary. The fracture surfaces were examined by scanning electron microscopy and the EDX spectrometer was applied for composition analysis of fracture surfaces. The substructure of martensite was studied by transmission electron microscopy. By addition of vanadium, fracture surfaces show mixed modes of intergranular and transgranular fracture and more Al content is found on the grain boundaries. For Ni-36.5at.%Al alloy, the planar faults observed in the martensite plates are the internal twins. By increasing the vanadium content, the modulated structure with stacking faults and dislocations dominates while the twinned martensite disappears. The stacking fault is determined to be extrinsic due to the substitution of V for Al. It is concluded that the segregation of sulfur on the high-energy state stacking fault area suppresses the intergranular fracture.

• Journal of the Korean Ceramic Society
• /
• v.36 no.1
• /
• pp.30-35
• /
• 1999

For dolomite clinkers used as stamp materials, the corrostion behavior of those by slag was inverstigated between 1550$^{\circ}C$ and 1650$^{\circ}C$. Fe2O3 among slag components was selectively penetrated into the grain boundaries of dolomite clinkers. In hot face, the magnesioferrite was preferentially formed by Fe2O3 component contained in dolomite clinker rather than Fe2O3 of slag. The corrosion steps of dolomite clinkers by slag were found as follows ; (1) The dicalciumferrite was formed by the reaction of the calcia within dolomite clinkers with Fe2O3 of slag. (2) The magnesia within dolomite clinkers reacted with the dicalciumferrite to from magnesioferrite and the residual calcia within dolomite clinkers reacted with the dicalciumferrite to form magnesioferrite and the residual calcia was dissolved into slag. (3) The magnesioferrite was corroded by CaO-SiO2 compounds of slag. With the temperature of slag increased, the magnesioferrite layer in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness and grain sizes of magnesioferrite was increased for dolomite clinker with Fe2O3.

• Analytical Science and Technology
• /
• v.5 no.1
• /
• pp.121-126
• /
• 1992

Transmission electron microscopy was used to investigate the structure of GaAs ${\Sigma}=19$, [110] tilt grain boundaries. Relative positions of Ga and As atoms in each grain on either side of the boundaries were determined by examining the dynamical coupling between HOLZ reflections and(200) beams. No inversion symmetry was present across the boundaries. These boundaries were observed to have a strong tendency to lie parallel to {331} planes. The atomic structure and lattice translation at these boundaries was studied in detail by high-resolution transmission electron microscopy(HRTEM). The boundary consists of units of 5-, 7-, and two 6-member rings.

• Korean Journal of Materials Research
• /
• v.2 no.6
• /
• pp.468-476
• /
• 1992

Stress rupture properties and fracture behavior of Ni microalloyed W were studied using direct load creep tester at 100$0^{\circ}C$, 110$0^{\circ}C$ and 120$0^{\circ}C$ in $H_2$. At the same grain size, 15${\mu}$m, the 100hr. stress rupture strength of W-0.4wt% Ni was 23% higher than that of W-0.2wt%Ni due to the grain growth during test. The minimum creep rate of W-0.2wt%Ni was decreased with an increase in initial grain size. By increasing the Ni content of Ni microalloyed W, rupture time was increased owing to the smaller number and size of cavity. All the specimens showed intergranular fracture by grain boundary sliding and nucleation, growth and coalescence of cavities at grain boundary.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.20 no.1
• /
• pp.23-29
• /
• 1984

Nowdays, the high strength aluminum alloys are broadly used for structural purpose, but the practical strengthening method by aging treatment are not much available. So that, in this study, in order to investigate the effect of aging treatment for strengthening on the fracture characteristics of the domestic high strength Al alloy (A2024BE), the variations of the aging temperature and time were taken after solution treatment. By microstructural examination, and by SEM fractographs of the fractures, the effects of aging temperature and time were investigated, considering on the fracture behaviour. The results obtained are as follows: 1) It was confirmed by microstructural investigation that the aging temperature of $190^{\circ}C$ and the aging time of 12hours were optimal to get more sound microstructure with distribution of uniform precipitation. 2) By step aging treatment, the proper aging time for obtaining the similar microstructure without any microstructural defects could be shortened in half the normal aging time. 3)By examining the SEM fractographs of the fracture surface, it was found that, regardless of the aging treatment time and temperature, all were intergranular ductile fractures, but the aging treatment at $190^{\circ}C$ for 12 hours resulted in dimple-type-transgranular and intergranular-ductile-frature.

• Korean Journal of Crystallography
• /
• v.4 no.2
• /
• pp.92-99
• /
• 1993

ZnO thin films were depositsd by Plasma enhanced CVD (PUW) using Diethylzinc and N2O gas, and micro-structue of ZnO thin films were investigated ZnO thin films composed of micro-crystallites was deposited at the substrate of loot. However, highly c-axis oriented ZnO thin films were deposited on the glass substrates above 200℃. TEM analysis revealed that an epitaxial (002) ZnO thin film was deposited on c-plane sapphire substrate at the substrate temperature of 350℃, and More patterns showing partial dislocation were observed at the grain boundary.

• Proceedings of the Korea Multimedia Society Conference
• /
• 2003.05b
• /
• pp.410-414
• /
• 2003

본 논문은 비디오 시퀀스에 카메라 패닝 보상과 2차원 시공간 엔트로피 임계법을 적용하여 추출한 객체포함영역을 대상으로 영상 분할을 수행하는 이동 객체 분할 기법에 관한 것이다. 우선, 웨이블렛 변환에 의해 구성한 피라미드 계층 구조상에서 카메라 패닝 벡터를 추정하여 전역 움직임을 보상한다. 이후, 전역 움직임이 보상된 기준영상을 대상으로 각 프레임간에서 2차원 시공간 엔트로피 임계법을 적용하여 이동 객체가 포함될 가능성이 있는 영역을 블록 단위로 추출한다. 다음으로, 2차원 시공간 엔트로피 입계법에 의해 분류된 영역을 토대로 각 블록을 움직임블록, 준 움직임 블록, 비 움직임 블록 중 어느 하나로 분류한 검색 테이블을 작성한다. 이어서, 검색 테이블을 참조하여 초기 탐색 계층 및 탐색 영역을 적응적으로 선정함으로써 피라미드 계층 구조상에서 효율적인 고속 움직임 추정을 수행하여 이동 객체에 해당하는 객체포함영역만을 추출한다. 최종적으로, 이렇게 추출된 객체포함영역에서 임계 기울기 영상을 정의한 후, 이를 기준 삼아 객체포함영역에 화소 단위의 형태학 기반 영상 분할 알고리즘을 적용함으로써 비디오 시퀀스에 포함된 이동 객체를 분할한다. 컴퓨터 시뮬레이션 결과를 통해 고찰할 때, 제안된 방법은 이동 객체에 대한 상대적으로 우수한 분할 특성을 제공할 수 있고, 특히 저대조 경계면의 분할 특성을 제고시키고 있음을 확인할 수 있다.