• 한국결정성장학회지
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• 제8권3호
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• pp.396-400
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• 1998

KLN은 성장 결정 내의 $Nb_2O_5$함유량에 따라 물성이 크게 변화하므로 단결정의 조성제어가 매우 중요하다. 본 실험에서는 초기 KLN용액의 $Nb_2O_5$함량을 증가시켜 $Nb_2O_5$함유량이 높은 KLN단결정을 온도요동법과 TSSG법에 의해 성장시키고 성장된 KLN단결정인 $Nb_2O_5$증가량에 따른 격자결함의 유무를 관찰하고자 유전 및 광학 특성을 관찰하다. KLN 단결정 내에 격자결함의 증가에 의해 낮은 에너지로의 단락 frequency 이동과 DPT 특성을 보이는 넓은 Curie 범위가 관찰되었다.

• 한국재료학회지
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• 제11권4호
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• pp.312-318
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• 2001

다발체 형성과 인발 공정으로 제조된 Cu-Nb 필라멘트 미세복합재료의 기계적 전기적 특성에 대하여 연구하였다. Nb의 함량이 증가함에 따라 강도는 점차 증가하였으나 연성은 Nb의 함량에 무관하였다. 293K와 75K에서의 항복강도의 비율은 Cu-Nb 미세복합재료의 Young의 계수 비율과 비슷하게 관찰되었다. 이러한 사실은 주로 장범위 방해물(athermal obstacles)들이 Cu-Nb 마세복합재료의 강도에 영향을 미친다는 것을 의미한다. 파면 조직관찰 결과는 Cu-Nb 미세복합재료는 Nb의 함량에 판관계없이 연성파괴의 특성을 나타내었으며, 부전선재 (subelematal wires)사이의 계면을 따라 발생하는 2차크랙 (secondary crack) 의 양은 Nb 함량이 증가함에 따라 증가하였다. 전기 전도도와 비저항비 (${\rho}_{293k}/{rho}_{75k}$)는 Nb 함량이 증가할수록 감소하였다. 이와 같은 Nb함량에 따른 전기전도도와 비저항비의 감소는 계면산란의 기여도가 증가하였기 때문이다.

• 한국재료학회지
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• 제31권12호
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• pp.682-689
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• 2021

NbC, HfC, TaC, and their solid solution ceramics have been identified as the best materials for ultrahigh-temperature ceramics. However, their structural stability and elastic properties are mostly unclear. Thus, we investigated structure and elastic properties of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C solid solutions via ab initio calculations. Our calculated results show that the stability of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C increases with the increase of Hf and Ta content, and (Nb_1-xHf_x)C is more stable than (Nb_1-xTa_x)C at the same content of Hf and Ta. The lattice constants decrease with increasing of Hf and Ta content. (Nb_1-xTa_x)C and (Nb_1-xHf_x)C carbides are mechanically stable and brittle. Bulk modulus of (Nb_1-xTa_x)C increases with increasing Ta content. In contrast, bulk modulus of (Nb_1-xHf_x)C decreases with increasing Hf content. Hardness of solid solutions shows the highest values at the (Nb_0.25Ta_0.75)C and (Nb_0.75Hf_0.25)C. In particular, (Nb_0.75Hf_0.25)C shows the highest hardness for the current system. The results indicate that the overall mechanical properties of (Nb_1-xHf_x)C solid solutions are superior to those of (Nb_1-xTa_x)C solid solutions. Therefore, controlling the Hf and Ta element and content of the (Nb_1-xTa_x)C and (Nb_1-xHf_x)C Solid solution is crucial for optimizing the material properties.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.336-338
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• 1991

Effects of $Nb_2O_5$ addition ranged from 0.0 to 0.75(wt%) on the microstructure and electrical porperties of PZT ceramics have been investigated. The Pb vacancy concentration increases with increasing NbO content. However, the experimental results show the resistivity increases with increasing $Nb^{5+}$ content. This behavior can be explained as a compensation effect and $Nb^{5+}$ can serve as a donar and contribute electrons to the conduction process. According to the law of mass action, this result may reduce the total charge carrier:thus the resistivity increase with NbO content in PZT.

• 소성∙가공
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• 제15권8호
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• pp.581-585
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• 2006

Effects of V on both the formation of Ti-Nb-V carbonitrides and mechanical properties of Ti-Nb bearing low carbon HSLA steels were investigated. Hot rolling process was simulated by using Gleeble 3500 system with the steels containing three different levels of V ($0{\sim}0.1wt.%$). Vanadium precipitated as Ti-Nb-V carbonitrides at austenite region but it did not precipitate as VC during austenite to acicular ferrite or bainitic ferrite phase transformation. As V content increased, the amount of Nb precipitates was decreased but the average size of Ti-Nb-V carbonitrides was increased due to larger diffusivity of V than that of Nb. Coarsened Ti-Nb-V carbonitrides could act as heterogeneous nucleation site during ${\gamma}{\rightarrow}{\alpha}$ phase transformation, thus, acicular ferrite transformation was promoted as V content increased, resulting in increase of upper shelf energy.

• Corrosion Science and Technology
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• 제12권1호
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• pp.34-39
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• 2013

In this study, the effect of niobium addition on the passivation behavior of Ti alloys in NaCl solution was investigated using various electrochemical methods. An ${\alpha}$-phase in Ti alloy was transformed into a ${\beta}$-phase and martensite structure decreased as Nb content increased. The corrosion and passivation current density($+300mV_{SCE}$) decreased as Nb content increased, and thereby a stable passive film was formed on the Ti alloy. Potential of Ti-xNb alloy in the passive region increased, whereas, current density decreased with time from results of potentiostatic and galvanostatic tests. Also, the corrosion morphology showed the smaller pits as Nb content increased. Consequently, Ti alloy contained high Nb content showed a good resistance to pitting corrosion in 0.9% NaCl solution.

• 한국재료학회지
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• 제17권8호
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• pp.442-446
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• 2007

Microwave dielectric properties of $0.85CaWO_4-0.15LnNbO_4$ (Ln = La, Sm) ceramics were investigated as a function of the sintering temperature and $Li_2WO_4$ content from 0.8 wt.% to 1.5 wt.%. A single phase with tetragonal scheelite structure was obtained at a given composition ranges. For the specimens with $Li_2WO_4$, the sintering temperature could be effectively reduced from $1150^{\circ}C$ to $900^{\circ}C$ due to the enhancement of sinterability. Dielectric constant (K) of the specimens with $LaNbO_4$ and $SmNbO_4$ was increased with the increase of sintering temperature and/or $Li_2WO_4$ content. However, K of the specimens with $LaNbO_4$ was higher than that of $SmNbO_4$ due to the larger dielectric polarizability $(\alpha)$ of $LaNbO_4$ ($18.08{\AA}$) than that of $SmNbO_4$ ($16.75{\AA}$). With an increase of $Li_2WO_4$ content, Qf value of the specimens with $SmNbO_4$ was decreased, while that of the specimens with $LaNbO_4$ was increased. Temperature coefficient of resonant frequency (TCF) was increased with the increase of $Li_2WO_4$ content.

• 열처리공학회지
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• 제16권5호
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• pp.260-266
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• 2003

In order to study the interfacial reaction between Nb thin sheet and Fe-C-(Si) alloy with different Chemical compositions, they were cast-bonded. The growth of carbide layer formed at the interface after isothermal heat treatment at 1173K, 1223K, 1273K and 1323K for various times was investigated. The carbide formed at the interface was NbC and the thickness of NbC layer was increased linearly in proportional to the heat treating time. Therefore, It was found that the growth of NbC layer was controlled by the interfacial reaction. The growth rate constant of NbC layer was slightly increased with increase of carbon content when the silicon content is similar in the cast irons. However, as silicon content increases with no great difference in carbon content, the growth of NbC layer was greatly retarded. The calculated activation energy for the growth of NbC layer was varied in the range of 447.4~549.3 kJ/moI with the compositions of cast irons.

• Corrosion Science and Technology
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• 제2권3호
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• pp.117-126
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• 2003

Due to excellent corrosion resistance and mechanical properties, austenitic stainless steel is widely used as the material for chemical plants. nuclear power plants, and food processing facilities. But, the zone affected by heat in the range of 400 to $800^{\circ}C$ during welding loses corrosion resistance and tensile strength since Cr-carbide precipitation like $Cr_{23}C_6$ forms at the grain boundary and thereby takes place the intergranular corrosion. In this study, AISI 304 stainless steel with the added Nb of 0.3 to 0.7 wt% was solutionized at $1050^{\circ}C$ and sensitized at $650^{\circ}C$. Specimen was welded by MIG. The phase and the microstructure of the specimens were examined by an optical microscope, a scanning electron microscope, and a x-ray diffractometer. The corrosion characteristics of specimens were tested by electrolytic etching and by double loop electrochemical potentiokinetic reactivation method(EPR) in the mixed solution of 0.5M $H_2SO_4$ + 0.01M KSCN. The melting zone had dendritic structure constituted of austenitic phase and $\delta$-ferrite phase. Cr carbide at the matrix did not appear, as Nb content increased. At the grain boundaries of the heat affected zone, the precipitates decreased and the twins appeared. The hardness increased, as Nb content increased. The hardness was highest in the order of the heat affected zone>melted zone>matrix. According to EPR curve, as the Nb content decreased, the reactivation current density(Ir) and the activation current density(la) were highest in the order of the melted zone

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 추계학술발표회요약집
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• pp.261.2-261
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• 1999