• 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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.657-661
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• 2002

PZT powder was prepared by partial oxalate method using $(Zr_{0.53}Ti_{0.47})O_2$, $Pb(NO_3)_2$ and $(COOH)_2{\cdot}2H_2O$ as a precipitant. $Nb_2O_5$ additive effect on microstructure and piezoelectric properties of PZT ceramics were investigated. The coexistence of rhombohedral and tetragonal phases of PZT ceramics at the sintering temperature of $1100^{\circ}C$ was revealed from the X-ray diffraction patterns. The grain size PZT ceramics was decreased with the increase $Nb^{5+}$. and the sinterbility of PZT ceramics was decreased with the increase $Nb^{5+}$ addition. The electromechanical coupling factors $K_p$ show above 0.60 at $1100^{\circ}C$ sintering temperature by $Nb_2O_5$ addition above 0.6mol%.

• 열처리공학회지
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• 제16권2호
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• pp.83-89
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• 2003

As a research for developing fine-grained high strength low carbon steels, the effects of austenitization temperature and hot deformation on microstructure was investigated in 0.15 wt.% carbon steels with microalloying elements such as Nb and Ti. When the steels were reheated at $1250^{\circ}C$, Nb containing steel showed very coarse austenite grain size of $200{\mu}m$ whereas Nb-Ti steel did fine one of $70{\mu}m$ because Ti carbonitrides could suppress the austenite grain growth. In case of 50% reduction at $850^{\circ}C$, the austenite grains in the Nb steel partially recrystallized while those in the Nb-Ti steel fully recrystallized probably due to finer prior austenite grains.For the Nb-Ti steel, ferrite grain size was not sensitively changed with austenitization temperature and compression strain and, severe deformation of 80% reduction was not essentially necessary to refine ferrite grains to about $3{\mu}m$ which could be obtained through lighter deformation of 40% reduction.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.216-217
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• 2005

In this paper, in order to develop Pb-free piezoelectric ceramics, $(Li_{0.05}Na_{0.57}K_{0.38})NbO_3$ ceramic was fabricated with the variation of $Bi_2O_3$ addition. Piezoelectric properties of the ceramic were varied with the amount of $Bi_2O_3$ addition and showed the maximum kp value at.0.2 wt% $Bi_2O_3$ addition. Qm of $Bi_2O_3$ added ceramics showed lower values than the non-added ceramics, however, the kp was increased by the addition of $Bi_2O_3$ up to 0.2 wt%. At the sintering temperature of 1110$^{\circ}C$ and the calcination temperature of 850$^{\circ}C$, the optimal values of density=4.52g/$cm^3$, kp=0.47, $\varepsilon_r$=400 were obtained.

• 한국세라믹학회지
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• 제25권5호
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• pp.488-494
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• 1988

Effects of MnO2 addition on themicrostructure, dielectric and piezoelectric properties of Rhombohedral, Tetragonal and Morphotropic phase boundary(MPB) in Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system were investigated and respectively the amount of MnO2 addition was 0, 0.2, 0.5, 1.0, 3.0wt%. In the tetragonal region, compared with the Rhombohedral and Morpotropic phase boundary, Mechanical quality factor(Qm), Curie temperature(Tc) and Dissipation factor were promoted by addition of MnO2. According to the results of the microstructure, dielectric and piezoelectric properties, the solid solution range of MnO2 addition in this system was 0.2-0.5wt%.

• 한국재료학회지
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• 제21권3호
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• pp.161-167
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• 2011

The stress-strain responses and oxidation properties of cold-rolled Zr-1.5Nb-O and Zr-1.5Nb-O-S alloys were studied. The U.T.S. (ultimate tensile strength) of cold-rolled Zr-1.5Nb-O-S alloy with 160 ppm sulfur (765 MPa) were greater than that of Zr-1Nb-1Sn-0.1Fe alloy (750 MPa), achieving an excellent mechanical strength even after the elimination of Sn, an effective solution strengthening element. The addition of sulfur increased the strength at the expense of ductility. However, the ductile fracture behavior was observed both in Zr-Nb-O and Zr-Nb-O-S alloys. The beneficial effect of sulphur on the strengthening was observed in the cold rolled Zr-1.5Nb-O-S alloys. The activation volume of cold-rolled Zr-1.5Nb decreased with sulfur content in the temperature region of dynamic strain aging associated with oxygen atoms. Insensitivity of the activation volume to the dislocation density and the decrease of the activation volume at a higher temperature where the dynamic strain aging occurs support the suggestion linking the activation volume with the activated bulge of dislocations limited by segregation of oxygen and sulfur atoms. The addition of sulfur was also found to improve the oxidation resistance of Zr-Nb-O alloys.

• 한국전기전자재료학회논문지
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• 제22권6호
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• pp.489-494
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• 2009

In this study, In order to improve dielectric and piezoelectric properties of Lead-free piezoelectric ceramics, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3+0.2\;wt%Ag_2O+0.4\;wt%MnO_2+Xwt%CuO$ were investigated as a function of the amount of CuO addition. With increasing the amount of CuO addition, density was increased up to 0.4 wt.% CuO and then decreased above. And also, electro mechanical coupling factor ($k_p$) was decreased. At the 0.4 wt% CuO added specimen sintered at $1020^{\circ}C$, $k_p$, Qm, density, dielectric constant (${\varepsilon}_r$) and $d_{33}$[pC/N] showed the optimal value of $4.37\;g/cm^3$, 0.354, 305, 645, and 144 pC/N respectively.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제3권1호
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• pp.35-39
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• 2000

The present study dealt with the relationships among the interfacial shear strength, the thickness of interfacial reaction layer and the impact value of $Nb/MoSi_2$ laminate composites. In addition, the tensile test was conducted to evaluate the fracture strain of $Nb/MoSi_2$ laminate composites. To change the thickness of the reaction layer, $Nb/MoSi_2$ laminate composites alternating sintered MoSi2 layers and Nb foils were fabricated as the parameter of hot press temperature. It has been found that the growth of the reaction layer increases the interfacial shear strength and decreases the impact value by localizing a plastic deformation of Nb foil. There also exist appropriate shear strength and the thickness of the reaction layer, which are capable of maximizing the fracture energy of $Nb/MoSi_2$.

• 한국재료학회지
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• 제11권5호
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• pp.345-353
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• 2001

본 연구에서는 MA 방법을 사용하여 $Al_3$Nb 금속간화합물의 조성에 Zr을 첨가하여 $Al_3$(Nb$_{1-x}$ )Zr$_{x}$ 합금분말을 제조한 후 이에 따른 상변화 거동 및 미세구조특성을 분석하였다. MA는Al$_3$(Nb$_{1-x}$ )Zr$_{x}$의 조성으로 Al, Nb, Zr 원료분말과 arc meltinly된 $Al_3$Nb, $Al_3$Zr 금속간화합물 분말을 사용하여 300rpm의 회전속도로 20시간 동안 MA하였다. 이때의 정상상태의 원료분말은 약 4$\mu\textrm{m}$의 평균입도와 약 12~18nm의 결정립크기를 가졌으며, arc melting된 분말은 약 2$\mu\textrm{m}$의 평균입도와 약 14nm의 결정립크기를 가지는 분말을 얻을 수 있었다 원료분말과 금속간화합물 분말의 MA 기구는 상이한 거동을 나타내었으며, 분말의 내부변형량은 원료분말이 금속간화합 분말보다 내부변형량이 더 많이 축적되었다. 이는 원료분말의 MA 경우 냉간 압접과 파괴가 반복적으로 진행되었지만 금속간화합물 분말은 취약한 화합물상이어서 냉간압접 보다는 파괴가 지배적으로 진행되었기 때문이다. 원료분말을 MA하였을 경우에는 Al (Nb.Zr)$_2$상이 형성되었으나 금속간화합물 분말로 MA하였을 경우에는 3원계 화합물상이나 비정질상으로 상변태 되지 않고 단지 두 합금상이 분쇄되어 나노복합화 되었다. 후속 열처리에 의해 원료분말인 경우에는 $Al_3$(Nb.Zr)의 화합물상이 쉽게 형성되었으나, 금속간화합물 분말의 경우에는 새로운 상 생성은 얼었고 단지 열처리 전의 분말내부에 쌓여있던 내부변형에너지가 약 60% 정도 감소하였다.

• 한국전기전자재료학회논문지
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• 제22권11호
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• pp.925-929
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• 2009

In this study, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3$ ceramics were investigated as a function of the amount of $Ag_2O$ addition in order to improve dielectric and piezoelectric properties of lead-free piezoelectric ceramics. With increasing the amount of $Ag_2O$ addition, density and electromechanical coupling factor ($k_p$) increased up to 0.2 wt.% $Ag_2O$ and decreased above 0.2 wt.% $Ag_2O$. At the sintering temperature of $1020^{\circ}C$, electromechanical coupling factor ($k_p$), density, dielectric constant (${\varepsilon}r$) and curie temperature (Tc) of ceramics with 0.2 wt% $Ag_2O$ showed the optimal values of 0.42, $4.33\;g/cm^3$, 738 and $393^{\circ}C$, respectively.