• Korean Journal of Materials Research
• /
• v.12 no.5
• /
• pp.375-381
• /
• 2002

N-type ${\beta}-FeSi_2$ with a nominal composition of $Fe_{0.98}Co_{0.02}Si_2$ powders has been produced by mechanical alloying process and consolidated by vacuum hot pressing. As-milled powders were of metastable state and fully transformed to ${\beta}-FeSi_2$ phase by subsequent isothermal annealing. However, as-consolidated $Fe_{0.98}Co_{0.02}Si_2$ consisted of untransformed mixture of ${\alpha}-Fe_2Si_ 5$ and $\varepsilon$-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting ${\beta}-FeSi_2$ phase. The transformation behavior of ${\beta}-FeSi_2$ was investigated by utilizing DTA, a modified TGA under magnetic field, SEM, and XRD analyses. Isothermal annealing at $830^{\circ}C$ in vacuum led to the thermoelectric semiconducting ${\beta}-FeSi_2$ phase transformation, but some residual metallic $\alpha$ and $\varepsilon$ phases were unavoidable even after prolonged annealing. Thermoelectric properties were remarkably improved by isothermal annealing due to the transformation from metallic $\alpha$ and $\varepsilon$ phases to semiconducting phases.

• Journal of Industrial Technology
• /
• v.21 no.B
• /
• pp.331-339
• /
• 2001

Zero to tension fatigue tests and strain controlled fatigue tests were carried out to find how initial strain induced martensite, ${\alpha}^{\prime}$ affects low and high cycle fatigue behavior and fatigue crack growth mechanisms. Microscopic study and phase analysis were carried out with TEM, SEM, EDAX, Optical Microscope, Ferriscope, and X-ray diffractometry. The amount of Initial ${\alpha}^{\prime}$ was controlled from 0% to 33% by controlling the temperatures for cold working and heat treatment. Lower contents of initial ${\alpha}^{\prime}$ showed higher fatigue resistance in low cycle fatigue but lower fatigue resistance in high cycle fatigue because it is ascribed to the more transformation of ${\alpha}^{\prime}$ martensite during low cycle fatigue and higher ductility. In high cycle fatigue, fatigue life is attributed to the strength and phase transformation of austenite into ${\alpha}^{\prime}$ during fatigue was negligible. ${\gamma}$ boundary, ${\gamma}/twin$ boundary, and ${\gamma}/{\alpha}^{\prime}$ boundary were found to be the preferred site of fatigue crack initiation.

• Korean Journal of Materials Research
• /
• v.10 no.1
• /
• pp.29-33
• /
• 2000

The amorphous tungsten nitrides, WNx, film could be fabricated by reactive sputtering process. The nitrogen concentration for the amorphization ranges from 10 at% to 40at%. The amorphous $W_{67}N_{33}$ film was crystallized into low resistivity $\alpha$-tungsten phase with equiaxed grains and excess nitrogen after the rapid thermal annealing for 1min at 1273K, which was similar to the resistivity of the sputtered pure tungsten film. The excess nitrogen was depleted from $\alpha$-tungsten crystals and then segregated at $\alpha$-tungsten/poly-Si interface. The segregated nitrogen has favored the formation of the homogeneous diffusion barrier layer comprised of silicon nitride, $Si_3N_4$, nano-crystals, which undertaken the inhibition of the high resistivity tungsten silicide reaction.

• Asian-Australasian Journal of Animal Sciences
• /
• v.13 no.8
• /
• pp.1059-1062
• /
• 2000

The objective of the investigation was to study the effect of intramuscular $PGF_2\;{\alpha}$ and GnRH on estrus behavior and ovarian response in Murrah buffalo heifers. Twelve Murrah buffalo heifers at 32 months of age that had not exhibited behavioral estrus symptom were included in the experiment. Out of 12,4 heifers were in follicular phase (plasma estradiol $57.05{\pm}12.52pg/ml$), another 4 heifers were in luteal phase (Plasma progesterone $2.24{\pm}0.25ng/ml$) while the ovaries of remaining four heifers were inactive (estradiol $23.70{\pm}1.66pg/ml$and progesterone $0.32{\pm}0.06ng/ml$). $PGF_2\;{\alpha}$ (25 mg, Lutalyse, im) and GnRH (200 ug, Fertagyl, iv) was administered to each heifer at interval of 10 days. The plasma progesterone concentration decreased within 48 hrs after $PGF_2\;{\alpha}$ injection and followed thereafter with follicular growth, estrus and ovulation. GnRH administration induced follicular growth, elevation of plasma estradiol concentration with subsequent exhibition of behavioral estrus in 2 out of 4 heifers having inactive ovary. The observation reveals that Murrah buffalo heifers at 32 months of age have developed receptors for $PGF_2\;{\alpha}$ and GnRH on ovarian and pituitary tissue respectively and response the single injection of $PGF_2\;{\alpha}$ and GnRH similar to the mature cycling animals.

• Proceedings of the Korea Society of Poultry Science Conference
• /
• 2003.11a
• /
• pp.82-83
• /
• 2003

To study effect of bean extracts to lessen the growth-suppressing-effect of krill meal diet, dietary krill meal with bean extracts on the performance of broiler chicks and proliferation of splenocytes and peripheral blood mononuclear cells(PBMC) and levels of circulating TNF-$\alpha$ and ovotransferrin in plasma was assayed. The krill meal with bean extracts diet lessened the growth-suppressing effect of the krill meal diet. During acute phase responce, the krill meal with bean extracts diet decreased the proliferation of splenocytes and increased the proliferation of the PBMC and reduced the circulating levels of TNF-$\alpha$ and ovotransferrin in plasma. The results Indicated that the krill meal with bean extracts diet related with the acute phase response in broiler chicks.

• Proceedings of the Korean Nuclear Society Conference
• /
• 2001.10a
• /
• pp.248.2-248
• /
• 2001

• Korean Journal of Materials Research
• /
• v.10 no.9
• /
• pp.636-641
• /
• 2000

The effects of Fe and V content on the characteristics of $\beta$ to $\alpha$ phase transformation for Zr-0.8Sn alloys were studied by optical and transmission electron microscopy. With increasing V content, $\beta{\rightarrow}\alpha+\beta$ transformation temperature decreased, thus allowing the width of $\alpha$-lath to be fine air-cooled Zr-0.8Sn-xV alloys. The width of $\alpha$-lath, however, was slightly increased with Fe content. While the $\beta$ to $\alpha$ transformed microstructures of water-quenched Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V and Zr-0.8Sn-0.2V were mainly slipped martensite, that of water-quenched Zr-0.8Sn-0.4V was predominantly twinned martensite. The transition of slipped martensite to twinned martensite in Zr-0.8Sn-Xv was thought to be due to the decrease of $M_S$ temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.355-356
• /
• 2009

The change of thermal expansion and mechanical behaviors by cold working has been investigated in Fe-29%Ni-17%Co low thermal expansion Kovar alloy. Fe-29%Ni-17%Co alloy was cold rolled gradually and prepared to plates having reduction ratio of 0%, 20%, 40%, 60%, and 80%. Annealing effect on the properties was also studied. Thermal expansion was measured from $25^{\circ}C$ to $600^{\circ}C$ with a heating rate of $5^{\circ}C$/min by using vacuum differential dilatometer. It was found that thermal expansion coefficient ($\alpha_{30{\sim}400}$) slightly decreased (reduction ration of 20%) and then remarkably increased (above reduction ration of 40%) with increasing reduction ratio of cold rolling. Thermal expansion coefficient ($\alpha_{30{\sim}400}$) was sharply decreased after annealing heat-treatment. Yield and tensile strengths were continuously increased and elongation was decreased by cold roiling. Microstructural observation and X-ray diffraction analysis results showed that the $\alpha$ phase significantly increased as the reduction ratio increased. The slight decrease of thermal expansion coefficient bellow reduction ration of 20% could be explained by the destroying short-range ordering and the decreasing of grain size. The significant increase of thermal expansion coefficient with cold rolling mainly attributed to the appearance of $\alpha$ phase. The correlation between the microstructural cause and invar phenomena for the low thermal expansion behavior was also discussed.

• Journal of the Korean Magnetics Society
• /
• v.9 no.3
• /
• pp.154-158
• /
• 1999

Magnetic properties and microstructure of nanocrystalline $\alpha$-(Fe, Co)-based Nd-(Fe, Co)-B-Nb-Cu alloys have been investigated. $Nd_x(Fe_{0.9}Co_{0.1})_{90-x}B_6Nb_3Cu_1$(x=2, 3, 4, 5, 6) alloys prepared by rapid solidification process show amorphous phase except the one with x=2. By a proper annealing, the amorphous in the alloy is changed to a nanocrystalline phase. It is confirmed that the nanocrystalline alloys are composed of $\alpha$-(Fe, Co) and $Nd_2(Fe, Co)_{14}B_1$ phase. The optimally annealed $Nd_3(Fe_{0.9}Co_{0.1})_87B_6Nb_3Cu_1$ alloy shows the highest remanence of 1.55 T. The coercivity increases with the increase of Nd content The maximum coercivity of 4.6 kOe is obtained from an optimally annealed $Nd_6(Fe_{0.9}Co_{0.1})_84B_6Nb_3Cu_1$ alloy, resulting in the maximum energy product of 10.6 MGOe.

• Journal of Powder Materials
• /
• v.9 no.6
• /
• pp.422-432
• /
• 2002

Mechanically driven decomposition of intermetallics during mechanical milling(MM 1 was investigated. This process for Fe-Ce and Fe-Sn system was studied using conventional XRD, DSC, magnetization and alternative current susceptibility measurements. Mechanical alloying and milling form products of the following composition (in sequence of increasing Gecontent): $\alpha$(${\alpha}_1$) bcc solid solution, $\alpha$+$\beta$-phase ($Fe_{2-x}Ge$), $\beta$-phase, $\beta$+FeGe(B20), FeGE(B20), FeGe(B20)+$FeGe_2$,$FeGe_2$,$FeGe_2$+Ge, Ge. Incongruently melting intermetallics $Fe_6Ge_5$ and $Fe_2Ge_3$ decompose under milling. $Fe_6Ge_5$ produces mixture of $\hat{a}$-phase and FeGe(B20), $Fe_2Ge_3$ produces mixture of FeGe(B20) and $FeGe_2$ phases. These facts are in good agreement with the model that implies local melting as a mechanism of new phase for-mation during medchanical alloying. Stability of FeGe(B20) phase, which is also incongruently melting compound, is explained as a result of highest density of this phase in Fe-Ge system. Under mechanical milling (MM) in planetary ball mill, FeSn intermetallic decomposes with formation $Fe_5Sn_3$ and $FeSn_2$ phases, which have the biggest density among the phases of Fe-Sn system. If decomposition degree of FeSn is relatively small(<60%), milled powder shows superparamagnetic behavior at room temperature. For this case, magnetization curves can be fitted by superposition of two Langevin functions. particle sizes for ferromagnetic $Fe_5Sn_3$ phase determined from fitting parameters are in good agreement with crystalline sizes determined from XRD data and remiain approximately chageless during MM. The decomposition of FeSn is attributed to the effects of local temperature and local pressure produced by ball collisions.