• Korean Journal of Materials Research
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• v.26 no.10
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• pp.535-541
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• 2016

The present study deals with the effects of micro-alloying elements such as Ni, V, and Ti on the recrystallization behavior of carbon steels at different strain rates. Eight steel specimens were fabricated by varying the chemical composition and reheating temperature; then, a high-temperature compressive deformation test was conducted in order to investigate the relationship of the microstructure and the recrystallization behavior. The specimens containing micro-alloying elements had smaller prior austenite grain sizes than those of the other specimens, presumably due to the pinning effect of the formation of carbonitrides and AlN precipitates at the austenite grain boundaries. The high-temperature compressive deformation test results indicate that dynamic recrystallization behavior was suppressed in the specimens with micro-alloying elements, particularly at increased strain rate, because of the pinning effect of precipitates, grain boundary dragging and lattice misfit effects of solute atoms, although the strength increased with increasing strain rate.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1691-1698
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• 1989

Gas sensing effects produced by adsorptive reaction between specimen surface and gases are expected to be influenced greatly by the state of the speimen surface. In this study, Co1-xMgxO ceramics oxygen sensors were prepared by pressing at 0.3-1.5ton/cm\ulcornerwith or without binder, intending to change porosity and average grain size on the surface purposely. The composition ratio of CoO to MgO was fixed at 1:1(mol.%). Microstructure of prepared Co0.5Mg0.5O ceramics were observed, the electrical properties and the sensitivity characteristics for oxygen gas were investigated in the device temperature range of 700-1000\ulcorner and for oxygen partical pressure range of 1-10**-4 atm. Temperature dependence of the resistivity of the specimen showed NTC behavior, average grain size increased and porosity decreased with increasing compaction pressure. The slope of the resistivity of the specimen on the oxygen partial pressure decreased with increasing average grain size and with decreasing porosity. Particularly, specimen pressed by 0.3 and 0.5 ton/cm\ulcornershowed the highest sensitivity to oxygen gas.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.453-459
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• 2003

In this study, the effect of heat treatment to the electrochemical polarization resistance for the Ti-6Al-4V alloy was measured. The solution heat treatments were carried out at $1066^{circ}E, 966^{\circ}$E$, followed by aging heat treated $550^{circ}E, 600^{circ}E, and 650^{circ}E$. The electrochemical polarization resistance behavior was measured by potentio-dynamic polarization in the 1N $HNO_3$ + 15ppm HF solution. The obtained results were as follows. 1. As solution heat temperature increased. the corrosion potential was increased, whereas passive current density and critical current density were decreased. 2. As aging heat temperature increased, the corrosion potential was almost constant, but passive current density was decreased 3. The results of composition test measured by EDS at grain boundary and near $\gamma'$ precipitates indicated that S, Cl. and Si which originated from base metal were segregated at the grain boundaries Al and Ti which were the main alloying element in $\gamma'$ were depleted at the $\gamma'$ precipitated. The depletion of Al and Ti in $\gamma'$ was caused to early breakdown of passive film.

• Journal of Magnetics
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• v.14 no.2
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• pp.71-74
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• 2009

The magnetic and structural properties of FINEMET (the Hitachi product name of the Fe-Si-B-Nb-Cu alloy) nanopowder with a composition of $Fe_{73.5}Si_{13.5}B_9Nb_3Cu_1$ atomic percent were investigated after annealing, chemical etching, and mechanical milling. The primary and secondary crystallization temperatures were 523 and $550^{\circ}C$, respectively. The grain size of the particles was adjusted by annealing time. Optimally annealed particles exhibited a homogenous microstructure composed of nanometer-sized crystalline grains. The grain boundary of the annealed particles was etched preferentially by chemical etching. Chemically etched particles were broken at the grain boundary by high-energy ball milling. As a result, a nanometer-sized FINEMET powder with a uniform size of crystalline grains was fabricated.

• Journal of Powder Materials
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• v.11 no.2
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• pp.137-142
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• 2004

In this study, chemical solution mixing and hydrogen reduction method was used to fabricate nanostructured $Fe_xCo_{1-x}$ alloy powders. Fe-Co chloride mixture, FeCl$_2$ and COCI$_2$ with 99.9％ purity, were reduced in hydrogen atmosphere. Nanostructured Fe-Co alloy powders with a grain size of 50 nm were successfully fabricated. Magnetic properties of fabricated $Fe_xCo_{1-x}$(x=0, 10, 30, 50, 70, 100) alloy powders with the same grain size were measured because size factor can affect magnetic properties. Coercivity of Fe-Co alloy powders were increased with increasing Co contents. Maximum value of coercivity in various Co contented Fe-Co alloy powders with similar grain size was 125 Oe at Fe$_{100}$. Saturation magnetization value at Fe$_{70}$Co$_{30}$ composition showed maximum value of 219 emu/g and saturation magnetization value decreased with increasing Co contents and minimum value of 155 emu/g was observed at Co$_{100}$.

• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.324-332
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• 1983

In this studies resistivity thermal expansion and microstructure of the Forsterite Porcelain as a high frequency insulator were investigated. The body containing Zn-glass shows higher resistivity than any other body. The bodies containing K, Ba, Cd-glass respectively consist of fine crystals of mosaic type. The bodies containing Bi, Zn, Zr-glass repectively included more large crystals because of the grain growth and coherence of fine particles In the 4 series Forsterite containing excess MgO 0-6% the thermal coefficients of the bodies increased with the increasing of excess MgO and the bodies have conspicuously high thermal expansion coefficients when 15% excess $BaCO_3$ was added to. The resistivities of additive bodies of $BaCO_3$ 0, 5, 10% in Forsterite containg excess MgO 2% are higher than any other that of composition. Bacause the growing of Forsterite crystals was restrained with the increasing of excess MgO $BaCO_3$ their grain size became fine and their grain boundaries were decomposed and also the glass phase having high refractive inder was increased. The higher the firing temperature increased the more the process of crystal growing was progressed.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.693-699
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• 2006

Textured $Bi_{0.5}(Na,K)_{0.5}TiO_3-BiFeO_3$ ceramics were prepared by the reactive-templated grain growth process, using platelike $Bi_4Ti_3O_{12}$ particles. The effects of chemical composition in $Bi_{0.5}(Na,K)_{0.5}TiO_3$ on texture development and densification were examined. Textured ceramics were obtained by using $Bi_{0.5}K_{0.5}TiO_3$ as an end member of the solid solution but densification was limited. Dense ceramics were obtained by using $Bi_{0.5}Na_{0.5}TiO_3$ but texture did not develop. Dense, textured ceramics were obtained by using $Bi_{0.5}(Na_{0.5}K_{0.5})_{0.5}TiO_3$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.328-331
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• 2000

The effect of the constituent elements and their composition of the seed layer on the properties of the evaporated Zn thin films was investigated. It was carried out by the analysis of the preferred orientation and the grain size, and the corrosion characteristics. Seed layers were prepared by evaporation of Al and AlCu respectively, and here the Cu content as additives of the source materials of seed layers were designed 5 a/o to 20 a/o. The values of full width at half maximum (FWHM) of the (002) x-ray diffraction peaks of Zn decreased by increasing the amount of the additives on Al seed layer, as a results, the grain sizes also decreased. In order to characteristics of Zn thin films evaporated on the various seed layers, electrical resistivity changes with a function of time at the temperature of 40$^{\circ}C$ and the relative humidity of 80%, as a result, the relative resistivity changes were increased by decreasing the grain size and the FWHM values of (002) peaks of Zn.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.4
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• pp.215-222
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• 2023

3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals, 3Y-TZP) ceramics are emerging as dental implant materials due to their superior optical and mechanical properties as well as excellent biophysical properties, in spite of low bioactivity. In this study, we investigated to sintered properties and microstructural defects of dental zirconia implants fabricated by ceramic injection molding and post-HIP (Hot isostatic pressing) processing and analyzed the processing parameters related with the obtainment of its high sinterd density. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of zirconia implants fabricated by injection molding were dependent on the fixtute size and implant type. Maximum sintered density of 99.2% and minimum grain size of 0.3-0.4 ㎛ were obtained from large-scaled 2-body sample. In 1-body ceramic implant, high sintered density of 99.5% was obtained, but it had a little monoclinic phase and wide grain size distribution.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.166-178
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• 2024

The localized corrosion resistance of UNS N07718 alloy was investigated after solution heat treatment. When the alloy was heat-treated at 1050 ℃ for 2.5 hours, it experienced an increase in average grain diameter, a reduction in grain boundary area, and the dissolution of delta phases along grain boundaries. Additionally, primary metallic nitrides (MN) and metallic carbides (MC), enriched with either Ti or Nb, were identified and exhibited a random distribution within the microstructures. Despite the solution heat treatment, the composition, diameter, and abundance of MNs and MCs remained relatively consistent. The critical pitting temperature (CPT), as determined by the ASTM G48-C immersion test, revealed similar values of 45 ℃ for both treated and untreated alloys. However, a decrease in maximum pit depth and corrosion rate was observed after the solution heat treatment. The microstructural changes that occurred during the heat treatment and their potential implications were discussed to understand the influence of the solution heat treatment.