• Journal of the Korean Society for Heat Treatment
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• v.36 no.5
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• pp.277-284
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• 2023

Hardness and damping characteristics of fine discontinuous precipitates (DPs) microstructure generated by low temperature long term isothermal aging were investigated in comparison with those of T6 heat-treated microstructure composed of DPs and continuous precipitates (CPs) in Mg-9%Al alloy. In this study, T6 and fine DPs microstructures were obtained by isothermal aging at 453 K for 24 h and at 413 K for 336 h, respectively, after solution treatment at 693 K for 24 h. The DPs microstructure exhibited higher hardness than the T6 microstructure, which is related to the lower (α + β) interlamellar spacing of the DPs. The DPs microstructure possessed better damping capacity than the T6 microstructure in the strain-amplitude independent region, whereas in the strain-amplitude dependent region, the reverse behavior was observed. The damping tendencies depending on strain-amplitude were discussed based on the microstructural features of the T6 and DPs microstructures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1270-1273
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• 2004

The combination of methane-chemical activation and Self-propagating High-temperature synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d < $1{\mu}m$ is developed. The specific feature of the technique is formation of the $YBa_2Cu_3O_{7-x}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples investigated.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.213-219
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• 2006

A Monte Carlo simulation based on Potts model in a three dimensional lattice was studied to analyze and design microstructures in porous sintered compacts such as porosity, pore size, grain (particle) size and contiguity of grains. The effect of surface energy of particles and the content of additional fine particles to coarse particles on microstructure development were examined to obtain fundamentals for material design in porous materials. It has been found that the larger surface energy enhances sintering (necking) of particles and increases contiguity and surface energy does not change pore size and grain size. The addition of fine particles also enhances sintering of particles and increases contiguity, but it has an effect on increment of pore size and grain size. Such a simulation technique can give us important information or wisdom for design of porous materials, e.g., material system with high surface energy and fine particle audition are available for higher strength and larger porosity in porous sintered compacts with applications in an automobile.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.462-470
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• 1995

The characteristics of spray-dried granules are important for dry pressing operation since they have great influences on die-filling, compaction ratio, and resulting green microstructure. An attempt was made to control granule morphology and the packing structure of fine Si3N4 particles in granules by adjusting suspension property. Mercury porosimetry was used to characterize the pore structures of both granules and green compacts. Finally, the effects of particle packing structure in granules and green microstructure on sintering behavior were investigated.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.209-216
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• 1995

In order to investigate the effect o green microstructure on the sintering behavior and properties of AlN ceramics, samples were prepared by slip casting and dry pressing. The slip cast samples had high green density, fine pore size and narrow pore size distribution. They showed much higher sinterability and more homogeneous sintered microstructure compared to the dry pressed samples. Both increased thermal conductivity and flexural strength for samples prepared by slip casting could be attributed to the improved microstructural homogeneity with isolated second phase(s).

• Journal of the Korean Society of Industry Convergence
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• v.24 no.5
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• pp.525-530
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• 2021

The purpose of this study was to investigate the effect of spherodizing heat treatment holding time on the microstructure and mechanical properties of the accelerated cooling-treated API X70 steel, which is mainly used as a structural material for line pipe steel for natural gas pipes. The accelerated cooling-treated API X70 steel was spherodizing treated at 700℃ for 12~48 h. The microstructure was observed using an OM and a FEG-SEM, and mechanical properties were obtained by tensile test. The microstructure of the API X70 steel was banded in the hot rolling direction, and the polygonal ferrite(PF) adjacent to pearlite(P) has mainly a fine size, and coarse PF and fine acicular ferrite were formed in the middle of P and P. As the spherodizing treatment time increased, the number of carbide particles decreased and its distribution interval increased, and the ferrite grain size was coarsened. The tensile strength decreased and the ductility increased with spherodizing treatment time, and the yield point elongation was disappeared in a stress-strain curve after the spherodizing treatment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.138-141
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• 2001

The evolution of lectures and microstructure during the warm-rolling and subsequent annealing in aluminum 3004 alloy sheets was investigated by employing X-ray texture measurements and microstructure observations. Whereas the typical $\beta$-fiber orientations with the strong Bs-orientation $\{112\}<110>$ formed in the normally cold-rolled specimen, the warm-rolling at $250^{\circ}C$ led to the development of a strong through thickness texture gradient which was characterized by shear texture at the surface layer and rolling textures at the center layer After warm rolling, ultra-fine grains formed in the thickness layer with shear texture components. Upon recrystallization annealing, the $\{001\}<100>$ Cube-texture developed at the expense of normal rolling texture components the rise to the formation of corase recrystallized grains. However, in the layer with shear texture components the continuous recrystallization took place and the fine grain size persisted even after recrystallization annealing.

• Journal of the Korean institute of surface engineering
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• v.17 no.2
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• pp.41-58
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• 1984

Zinc was electrodeposited from cyanide solutions at temperature from 20$^{\circ}C\;to\;40^{\circ}C$ in the range of current density from 0.5 to 8A/$dm^2$. The preferred orientation changed from (10.3)+(11.0) to (11.0) texture with increasing cathode overpotential in the additive free solution, while the (11.0) preferred orientation developed at lower overpotentials (800-1270 mV) and the (11.0)+(10.0) preferred orientation was formed at higher overpotential (1300-1400mV) in the solution with brightner. Mossy type of morphology developed mostly in the additive free deposits and the microstructure of the cross section of the above deposits changed from columar structure to granular structure with increasing overpotential. The surface appearance of the deposits with additive having (11.0) texture was the smooth deposit of very small crystallite, while that of the deposits having (11.0)+(10.0) texture was fine crystalline deposit. The microstructure of the cross section of them was the fine field oriented type of structure.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.469-471
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• 2006

The effects of $Cr_2O_3$ on the microstructural evolution and mechanical properties of $Al_2O_3$ polycrystalline were investigated. The microstructure of $Al_2O_3-Cr_2O_3$ composites (ruby) was carefully controlled in order to obtain dense and fine-grained ceramics, thereby improving their properties and reliability with respect to numerous applications related to semiconductor bonding technology. Ruby composites were produced by Ceramic Injection Molding (CIM) technology. Room temperature strength, hardness, Young's modulus and toughness were determined, as well as surface strengthening induced by thermal treatment and production of a fine-grained homogenous microstructure.

• International Journal of Korean Welding Society
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• v.3 no.2
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• pp.46-52
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• 2003

The refinement of microstructure and phase transformation near the interface of pure copper/carbon steel dissimilar metals joints with various friction welding parameters have been studied in this paper. The microstructure of copper and carbon steel joints were changed to be a finer grain compared to those of the base metals due to the frictional heat and plastic deformation. The microstructure of copper side experienced wide range of deformed region from the weld interface and divided into very fine equaxied grains and elongated grains. Especially, the microstructures near the interface on carbon steel were transformed from ferrite and pearlite dual structure to fine ferrite, grain boundary pearlite and martensite due to the welding thermal cycle and rapid cooling rate after welding. These microstructures were varied with each friction welding parameters. The recrystallization on copper side is reason for softening in copper side and martensite transformation could explain the remarkable hardening region in carbon steel side.