• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.937-938
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• 2006

Tungsten heavy alloys with different ratios of Mo and Ni-Fe matrix were liquid-phase-sintered to investigate their microstructural evolution. Results indicated that increased Mo in the alloy promoted the formation of a (W,Mo)(Ni,Fe) type intermetallic compound in the furnace-cooled condition. It was a monoeutectic reaction when the added Mo content was higher than 49at.%, or a eutectic reaction when this value was between 37at,% to 49at.%. When Mo was added between 25at.% to 37at.%, the precipitation of the intermetallic compound took place by either a eutectoid or peritectoid reaction.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.1029-1038
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• 1993

The microstructures of aluminas, included of dissolved CaO as $\alpha$-alumina seeded pseudo-boehmite hydrosol was gelled in plaster mold and doped of MgO as dipping of calcines(120$0^{\circ}C$-2h) into Mg-nitrate solution, were compared to the one of which additives are excluded during the gellation. It was formed the boundary layer of 300~350${\mu}{\textrm}{m}$ distance from surface to the inside, containing of approximately 500ppm CaO by dissolved Ca from plaster mold. As the MgO addition to the boundary layer with dissolved CaO, the microstructure of the layer was uniformed and inhibited the grian growth, compared to one of that additives be excluded specimen and of MgO doped-inside region. This result was considered as abnormal grain growth and effect of flat boundary formation be appeared by effects of dissolved CaO, were decreased by MgO co-doping.

• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.99-103
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• 1999

Compressive creep of dense polycrystalline $BaTiO_3$, with average grain sizes of 19.3-52.4$\mu\textrm{m}$, has been investigated at 1100-$1300^{\circ}C$ in air or under controlled atmospheres $(10^2-10^5Pa \;O_2)$. Some cavity growth occurred during deformation because of non-steady-state damage accumulation in the form of cavitation. Comparison of the creep data of polycrystalline BaTiO3 with existing diffusivity and creep data for perovskite oxides suggested that deformation of polycrystalline $BaTiO_3$ was controlled by the extrinsic lattice diffusion of barium or titanium.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.824-828
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• 1990

Zirconia gel fibers were fabricated by sol-gel processing using zirconium alkoxides and 2, 4-pentanedione. Their phase transformation and microstructural evolution were studied after heat treatments up to 150$0^{\circ}C$. Tetragonal ZrO2 began to form at 50$0^{\circ}C$ and followed by monoclinic, tetragonal phase during subsequent heat treatments at 1000, 150$0^{\circ}C$ for 1hour respectively. During cooling from 150$0^{\circ}C$, cracks were created, propagated along grain boundaries due to the volume change from tetragonal to monoclinic transformation.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.464-467
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• 1996

The microstructural evolution during mechanical alloying of Nb and Sn powders, of average composition Nb3Sn, has been investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). Observations by SEM showed a progressive change of milling time. From the XRD studies, the structural development with milling time depends on the ball size for a given powder/ball ratio. Using a larger ball of 9.5mm diameter, the elemental powders initially alloy mechanically to form an A15 structure phase, and then amorphised with continued milling. However, in case of milling with a smaller ball of 3.968mm diameter, an amorphous phase is first formed. These results can be understood by considering the dependence of the milling energy on the ball size. The homogeneous stoichiometric $Nb_3Sn$ phase could be easily obtained by heat treatment of a supersaturated solid solution produced by MA. Heat treatment of an amorphous phase formed by MA resulted in the mixture of the $Nb_3Sn$ and $Nb_6Sn_5$ phases.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.278-279
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• 2006

The increasing demand for automotive industries to reduce the weight of the vehicles has led to a growing usage of Al alloy powder metallurgy (P/M) parts. In order to control the sintered microstructure and mechanical properties of the aluminium alloy powder metallurgical (P/M) parts, it is essential to establish a fundamental understanding of the microstructural development during the sintering process. This paper presents a detailed study of the effect of temperature and initial starting materials on the evolution of microstructure during the sintering of Al-Cu-Mg-Si blends for PM.

• Journal of Korea Foundry Society
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• v.37 no.5
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• pp.157-163
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• 2017

In the present study, the microstructural evolution and deformation behavior of AA 2014 aluminum alloys with different microstructures in a semi-solid state were investigated. For a given alloy, applied load and deformation time, the measured strain was higher at a higher temperature, indicative of a lower solid fraction. When a large proportion of the liquid was present as intragranular droplets, the alloy would not as easily deform because the effective liquid fraction between the solid grains had decreased. Greater deformation was achieved with higher grain boundary misorientations due to the enhanced wetting of the grain boundaries with liquid. A semi-empirical constitutive model is proposed for semi-solid deformation under the conditions in the present study. The mechanism of semi-solid deformation incorporates the initial flow of the liquid in the early stages of deformation, followed by a more gradual increase in the strain due to deformation by grain sliding accompanied by self-diffusion in the solid grains.

• Korea-Australia Rheology Journal
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• v.17 no.4
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• pp.171-180
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• 2005

We present numerical results for inertialess elliptic particle suspensions in a Newtonian fluid subject to simple shear flow, using the sliding bi-periodic frame concept of Hwang et al. (2004) such that a particulate system with a small number of particles could represent a suspension system containing a large number of particles. We report the motion and configurational change of elliptic particles in simple shear flow and discuss the inter-relationship with the bulk shear stress behaviors through several example problems of a single, two-interacting and ten particle problems in a sliding bi-periodic frame. The main objective is to check the feasibility of the direct simulation method for understanding the relationship between the microstructural evolution and the bulk material behaviors.

• Metals and materials international
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• v.24 no.6
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• pp.1293-1302
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• 2018

Nanocrystalline (NC) Ni electrodeposits (EDs) with a mean grain size of $34{\pm}12nm$ has been investigated, from room temperature to $800^{\circ}C$ under a purge gas of argon, by both non-isothermal and isothermal differential scanning calorimetry measurements, in combination with characterization of temperature-dependent microstructural evolution. A significant exothermic peak resulting from superimposition of recrystallization and surface oxidation occurs between 340 and $745^{\circ}C$ at a heating rate of $10^{\circ}C/min$ for the NC Ni EDs. The temperatures for recrystallization and oxidation increase with increasing the heating rate. In addition, recrystallization leads to a profound brittle-ductile transition of the Ni EDs in a narrow range around the peak temperature for the recrystallization.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.718-719
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• 2006

Two different commercial aluminium powder grades have been densified by direct hot extrusion. The extrusion temperature was $425^{\circ}C$, with an extrusion ratio of 1:16. Prior to extrusion, some green compacts were pre-sintered ($500^{\circ}C$). The evolution of the extrusion load during the process and the hardness of the final products have been investigated. Additionally, microstructural characterization by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD) was carried out. The obtained results evidence grain refinement. Additionally, inter-metallic precipitation, dynamic recovery and geometric dynamic recrystallization take place depending on some process variables, powder composition, heat treatment, strain $\ldots$