• Journal of Welding and Joining
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• v.15 no.5
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• pp.92-103
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• 1997

The purpose of this study is to improve the wear resistance and hardness of Al alloy by making a formation of the thick surface hardening layers. The thick surface hardening layers were formed by PTAW(Plasma Transferred Arc Welding), with the addition of metal powders (Cu), ceramics powders (NbC, TiC), and mixture powders (Cu+NbC) in Al alloy (A1050, A5083). Mechanical properties of overlaid layers (wear resistance, hardness) were investigated in relation to the microstructure. The results obtained are summarized as follows: The depth of penetration was increased with increasing powder feeding rate. It is considered that these increase were due to the thermal pinch effect by the addition of powders, especially, for the Cu powders, were due to the heat of reaction with the matrix. The hardness and wear resistance of overlaid layers were improved with increasing powder feeding rate. For the Cu powders, it is considered that these increase were due to the increase of the formation of ${\theta}(CuAl_2)$ phase with increasing feeding rate of Cu powers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.4
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• pp.356-360
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• 2002

The piezoelectric properties of $0.05Pb(Al_{0.5}Nb_{0.5})O_3-0.95Pb(Zr_{0.52}Ti_{0.48})O_3+0.7wt%Nb_2O_5+o.5wt%MnO_2$ ceramics with the additive of BaCO$_3$were investigated. As the addition of BaCO$_3$increased from 0 to 0.4 wt%, the dielectric constant ($\epsilon^T _{33}$), piezoelectric constant ($d_33$), electromechanical coupling factor ($k_p$), and mechanical quality factor ($Q_m$) increased, while the dielectric loss ($tan\delta$) decreased. The highest piezoelectric and dielectric properties were observed at $1200^{\circ}C$ of the sintered temperature with 0.4 wt% of $BaCO_3$, and the properties of $d_33$, $k_p$, and $Q_m$ were 339 pC/N, 60% and 1754, respectively.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.377-381
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• 1997

Poling condition in 2 mol% MgO-doped $LiNbO_3$ crystals is investigated by varying the amplitude of poling electric field from 3V/cm to 7V/cm. It is found that 5V/cm is the best value for the formation of single domain by analysing the characteristics of the second harmonic generation(SHG) as the function of temperature. The temperature dependence of the phase-matching profile of SHG for the crystal applied by a spatially modulated electric field is observed to be very different from the simple sinc function. The distorted profile can be consistently fitted with the numerical simulations. This shows that the crystal homogeneity can be tested by the SHG temperature phase-matching profile. In addition, the thermo birefringence coefficient and electro birefringence coefficient of SHG were measured from the temperature dependence of phase-matching profile and shifts of phase-matching temperature by appling electric field along c-axis.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.1
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• pp.17-25
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• 1993

The Cu - $Nb_3Sn$ composites wire as a superconducting material was prepared by in situ method as follow: Cu - 15wt.% Nb alloys which were melted in a high -frequency induction furnace and casted in bar were cold-worked up to the final diameter of 0.24 mm, electroplated with Sn, pre-treated in two steps and then diffused at $550{\sim}650^{\circ}C$ for 24 ~ 96 hrs. The overall $J_c$ and $T_c$ of the specimens were measured by the four point-probe method at 10 K in the magnetic field of 0 Tesla. The overall $J_c$ of the composites wire which diffused at $550^{\circ}C$ after pre-treating in two steps were generally higher than those of the wire at either $600^{\circ}C$ or $650^{\circ}C$. For the specimens diffused at $550^{\circ}C$, the overall $J_c$ were increased until 72 hrs. of diffusion time and then decreased. However, in case of diffusion at $600^{\circ}C$ and $650^{\circ}C$, the overall $J_c$ were gradually decreased from the beginning. The maximum overall $J_c$ obtained in this experiment was $1.3{\times}10^4\;A/cm^2$, which was measured for the specimen diffused at $550^{\circ}C$ for 72 hrs. When the specimens were diffused at $550^{\circ}C$ for 72 hrs, after pre-treating, the measured critical temperature, $T_c$ was 16.19 K. Similar $T_c$ value were obtained in other specimens regardless of diffusion time and temperature.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.364-375
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• 1994

The microstructure of medium-carbon non-heat treated steels by air-cooling shows ferritepearlite structure. Compared to the conventional Q/T steels, the strength of these steels containing V, Nb and Ti are similar to Q/T steels. However, their toughness are inferior. In this study, the mechanical properties and microstructures of low-carbon Mo bearing steels produced by direct-quenching process were investigated. Especially, the effect of Mo on the direct-quenched steels was examined. The direct-quenched steels containing Mo were found to have higher strength and toughness. Mo seemed to be effective in producing the fine structure and dense precipitates because of decreasing transformation temperature. The best results were 1211 MPa in UTS and 127.5 J in toughness in the oil quenched 0.15C+O.llV+ 0.035Nb+ 1.81Mo steel. Compared to 0.4% C microalloyed steels, this results showed that UTS increased by 45% and toughness by 2 times.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.276-279
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• 2000

Ferroelectric properties of $SrBi_2TaNbO_9$ (SBTN) thin films were changed by the amount of Bi content in SBTN. We suggested that the addition of excess Bi into the films could be accomplished by heat-treating $SBTN/Bi_2O_3/SBTN$ heterostructure fabricated by r.f. magnetron sputtering method. Excess Bi composition was controlled by the thickness of the sandwiched $Bi_2O_3$ from 0 to $400\;\AA$. When the SBTN thin films were inserted by $400\;{\AA}\;Bi_2O_3$ layer, $Bi_2Pt$ phase was formed as a second phase in SBTN films, resulting in poor ferroelectric properties. The onset temperature for hysteresis loop can be reduced by heat treating $SBTN/Bi_2O_3/SBTN$ heterostructure. The films with $SBTN/Bi_2O_3(100\;{\AA})/SBTN$ hetero-structure followed by annealing at $650^{\circ}C$ for 30 min show 2Pr and Ec of $5.66\;{\mu}C/\textrm{cm}^2$ and 54 kV/cm, respectively.

• Korean Journal of Materials Research
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• v.24 no.2
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• pp.111-115
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• 2014

Titanium and its alloys are useful for implant materials. In this study, porous Ti-Nb-Zr biomaterials were successfully synthesized by powder metallurgy using a $NH_4HCO_3$ as space holder and $TiH_2$ as foaming agent. Consolidation of powder was accomplished by spark plasma sintering process(SPS) at $850^{\circ}C$ under 30 MPa condition. The effect of high energy milling time on pore size and distribution in Ti-Nb-Zr alloys with space holder($NH_4HCO_3$) was investigated by optical microscope(OM), scanning electron microscope(SEM) & energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). Microstructure observation revealed that, a lot of pores were uniformly distributed in the Ti-Nb-Zr alloys as size of about $30-100{\mu}m$ using mixed powder and milled powders. In addition, the pore ratio was found to be about 5-20% by image analysis, using an image analyzer(Image Pro Plus). Furthermore, the physical properties of specimens were improved with increasing milling time as results of hardness, relative density, compressive strength and Young's modulus. Particularly Young's modulus of the sintered alloy using 4h milled powder reached 52 GPa which is similar to bone elastic modulus.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1042-1045
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• 2001

Microwave dielectric properties of Ba(Zn$_{1}$3/Nb$_{2}$3/) $O_3$-Sr(Zn$_{1}$3/Nb$_{2}$3/) $O_3$(BZN-SZN) system were investigated as a function of sintering temperature and Zr $O_2$content. Density was increased and the temperature coefficient of resonant frequency (TCF, $\tau$$_{f}$) decreased with increasing sintering temperature. However dielectric constant (K) and Q$\times$f value did not change markedly with the sintering temperature. For the samples sintered at the same temperature, density, dielectric constant, and Q$\times$f value were increased and TCF was decreased with increasing Zr $O_2$concentration. Especially, the dielectric constant of the sample increased with x and exhibited the maximum value ($\varepsilon$$_{r}$=41) when x=0.6 at 1575$^{\circ}C$ sintered. TCF decreased with x and exhibited the minimum value ($\tau$$_{f}$=+0.8ppm/$^{\circ}C$) when x=1.0..0.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1040-1048
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• 1998

Ferroelectric properties of{{{{ { { { {SrBi }_{2 }Ta }_{2-x }Nb }_{x }O }_{9 } }} (SBIN) thin films were affected by the amount of Bi content in SBTN. The addition of Bi into the SBTN films could be accomplished by heat treating SBTN/Bi2O3/SBTN het-erostructures fabricated by r.f. magnetron sputtering method. The variation of Bi content was controlled by changing the thickness of the sandwiched Bi2O3 in SBTN/Bi2O3/SBTN heterostructure from 50 to 400$\AA$. As changing the thickness of the sandwiched Bi2O3 in Bi2O3 films was increased from 0 to 100$\AA$ the grain grew faster and the ferroelectric pro-perties were improved. On the other hand when the thickness of Bi2O3 films was thicker than 150$\AA$ the fer-roelectric properties were deteriorated Especially for SBTN thin films inserted by 400$\AA$ Bi2O3 layer a Bi2Phase appeared as a second phase resulting in poor ferroelectric properties. The maximum remanent po-larization (2Pr) and coercive field(Ec) were obtained for the SBTN/Bi2O3/(100$\AA$)/SBTN thin films. In this case 2Pr and Ec were 14.75 $\mu$C/cm2 and 53.4kV/cm at an applied voltage of 3V respectively.

• Analytical Science and Technology
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• v.10 no.1
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• pp.35-42
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• 1997

The sample pretreatment technique using a high pressure acid digestion bomb for the analysis of ceramic capacitor materials, such as barium titanate and PZT, was studied. When the concentrations of hydrochloric acid were varied with the addition of nitric acid or distilled water, quantitative measurements for those samples were carried out using inductively coupled plasma atomic emission spectrometry. From this experiment the results indicate that most of elements, such as Ba, Mn, Zn, Si, etc., aren't affected by the concentration of hydrochloric acid but Nb and Zr are very susceptable to it. It however turns out that the digestion time relatively gave little effects on the analytical result. In case of Nb the ratio of hydrochloric acid to water should be greater than 3:1(v / v) for the best analytical result. For the Pb determination use of diluted hydrochloric acid compared to the mixture of nitric acid and hydrochloric acid showed a better analytical result.