• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.250-257
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• 1997

The microstructure and magnetic properties of Fe-Nb-B-N thin film alloys, which produced by rf magnetron sputtering method in $Ar+N_2$ mixed gas atmosphere, were investigated. The $Fe_{70}Nb_{14}B_{11}N_5$ films, annealed at 59$0^{\circ}C$, exhibit soft magnetic properties: $4{\pi}M_s=16.5kG$ , $H_c=0.13Oe$ and ${\mu}_{eff}$ (1~10 MHz)=5, 000. The frequency stability of the Fe-Nb-B-N films has also been found to be good up to 10 MHz. The Fe-Nb-B-N thin film alloys annealed at 59$0^{\circ}C$ consist of three phase; fine crystalline $\alpha$-Fe phase with grain size of about 5~10 nm, Nb-B rich amorphous phase and Nb-nitride precipitates with the size of less than 3 nm. Annealed Fe-Nb-B films have two phases; $\alpha$-Fe grains with the size of about 10 nm and Nb-B rich amorphous phase. The addition of N decreased $\alpha$-Fe grain size due to the precipitation of NbN. The good magnetic properties of the Fe-Nb-B-N film alloys are due to fine $\alpha$-Fe grains resulting from the precipitation of NbN.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.435-438
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• 2012

As lead-free piezoelectric materials, $Ag_2O$ doped $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3+x$ mol% (where x = 0, 0.5, 1, 1.5, 2, 2.5 and 3, respectively) ceramics were fabricated by a conventional sintering process. The doping effects on the microstructure and electrical properties of the $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3$ ceramics were systematically investigated. When the 3 mol % $Ag_2O$ doped $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3$ samples were sintered at $1,080^{\circ}C$ for 5 hrs in air, these ceramics showed excellent values of density=4.20 $g/cm^3$, piezoelectric constant ($d_{33}$)=174 pC/N and phase transition temperature$(T_c)=421.6^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.342-346
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• 2012

This work deals with the preparation of dense SiC based ceramics with high electrical conductivity without oxide sintering additives. SiC samples with different content of conductive Ti-NbC phase were hot pressed at $1850^{\circ}C$ for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of Ti-NbC in weight ratio of Ti/NbC 1:4. Composite with 50% of conductive Ti-NbC phase showed the highest electrical conductivity of $30.6{\times}10^3\;S{\cdot}m^{-1}$, while the good mechanical properties of SiC matrix were preserved (fracture toughness 4.5 $MPa{\cdot}m^{1/2}$ and Vickers hardness 18.7 GPa). The obtained results show that use of NbC and Ti as sintering and also electrically conductive additives is appropriate for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.

• Transactions on Electrical and Electronic Materials
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• v.8 no.5
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• pp.201-205
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• 2007

Low temperature sintering behavior and microwave dielectric properties of the $BiNbO_{4^-}$ and the $ZnNb_2O_{6^-}zinc$ borosilicate glass(ZBS) systems were investigated with a view to applying the composition to LTCC technology. The addition of $10{\sim}30$ wt% ZBS in both systems ensured successful sintering below $900^{\circ}C$. For the $BiNbO_{4^-}ZBS$ system, the sintering was completed when 15 wt% ZBS was added whereas 25 wt% ZBS was necessary for the $ZnNb_2O_{6^-}zinc$ system. Secondary phase was not observed in the $BiNbO_{4^-}ZBS$ system but a small amount of $ZnNb_2O_6$ with the willemite structure as the secondary phase was observed in the $ZnNb_2O_{6^-}ZBS$ system. In terms of dielectric properties, the application of the $BiNbO_{4^-}$ and the $ZnNb_2O_{6^-}ZBS$ systems sintered at $900^{\circ}C$ to LTCC were shown to be appropriate; $BiNbO_{4^-}15$ wt% ZBS($\varepsilon_r=25,\;Q{\times}f\;value=3,700GHz,\;\tau_f=-32ppm/^{\circ}C$) and $ZnNb_2O_{6^-}25$ wt% ZBS($\varepsilon_r=15.8,\;Q{\times}f\;value=5,400GHz,\;\tau_f=-98ppm/^{\circ}C$).

• Journal of the Korean Society for Heat Treatment
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• v.29 no.1
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• pp.15-23
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• 2016

The effects of austenitizing temperature and cooling rate on precipitation behavior and tensile properties were investigated in an Mn-Mo-Nb-V pressure vessel steel. During austenitizing, it was shown that the austenite coarsening was somewhat suppressed by undissolved NbC. After cooling from austenitizing, the microstructure of all the steels mainly consisted of upper bainite. However, the steel comprised a little lower bainite and martensite in the case of aqua oil quenching from $1000^{\circ}C$, which would be due to increased hardenability by partly dissolved Nb and comparatively large austenite grains. The average size of NbC in austenite at higher temperature was analyzed to be smaller than that at lower temperature because of the more dissolution. It was found that the NbC did not grow much during fast cooling from austenitizing. Meanwhile, the NbC grew much during slow cooling, probably due to wide temperature range of cooling and sufficiently long time for NbC to grow. It was conjectured the V precipitates newly formed and/or grew during cooling from austenitizing and during tempering. On the other hand, the formation of NbC was almost completed before tempering and little more precipitated during tempering. Among the tempered steels, the steel which was fast cooled from $1000^{\circ}C$ showed the highest tensile strength, which seemed to come from the microstructure of fine upper bainite and some low temperature phases as well as the comparatively fine NbC precipitates.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.96-97
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• 2015

확산을 이용한 표면 개질법인 Thermo-Reactive Diffusion(TRD) 기술 기반 2단 표면처리를 통해 고경도의 Nb(C,N) 코팅층을 고탄소 베어링강인 JIS-SUJ2강에 형성시켰다. 2단 표면처리는 암모니아 가스 질화와 분말 확산 코팅법으로 구성된 2step 열처리이다. 본 연구에서는 가스질화 화합물층의 두께가 코팅층 성장 거동에 어떤 영향을 미치는지 알아보기 위해서 $550^{\circ}C$에서 3, 6시간 암모니아 가스 분위기에서 가스질화를 실시하고, $900^{\circ}C$에서 3시간 분말 확산법을 통해 표면 코팅층을 형성하였다. 생성된 코팅층의 형상과 두께 측정을 광학현미경(OM) 과 주자전자현미경(SEM)을 통해 한 결과, 가스 질화는 약 10uu와 16um, 최종 코팅층은 약 정도 생성이 되었음을 확인하였다. 코팅층의 성분 분석은, EDS, FE-EPMA, XPS 분석을 통해서 실시하였다. EDS와 FE-EPMA 원소 mapping을 통해 모재에 비해 높은 농도의 Nb, C 그리고 N이 코팅층 내부에 존재함을 확인하였다. XPS분석의 결합에너지 peak를 통해 NbC, NbN 그리고 Nb-oxide가 생성이 되었음을 분석하였다. 생성된 코팅층의 경도는 low mode에서 10회 측정한 후 평균값을 내었고, 각각 Hv이었다.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.1-5
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• 2021

Among elemental metals, niobium (Nb) has the highest superconducting transition temperature (T_c) at ambient pressure. Thus, Nb films have been used in superconducting electronics and radio frequency cavity applications. In this study, the depositional factors determining the crystallinity and T_c of Nb films were investigated. An Nb film grown at a sputtering temperature of 240℃ exhibited the maximum crystallinity of Nb and the minimum crystallinity of niobium oxide. X-ray photoelectron spectroscopy confirmed a maximum atomic percent of niobium and a minimum atomic percent of oxygen. A sputtering power of 210 W and a sputtering time of 50 min were the optimal conditions for Nb deposition, and the T_c of the optimized film (9.08 K) was close to that of bulk Nb (9.25 K). Transmission electron microscopy images of the thick film directly confirmed the removal of the typical in-plane compressive strain in the (110) plane caused by residual stress.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.121-128
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• 1996

The optimum conditons were experimentally established for the powder synthesis and sintering of the feed-rods for $LiNbO_3$ crystal growth by a floating zone method. At the lower synthesis temperatures(700, $ 800^{\circ}C$) the minor amounts of $Li_2CO_3$ and $Nb_2O_5$ were present in the synthesized $LiNbO_3$ powder and at the higher temperature the particle size increased which is not favorable for the sintering process for the feed-rods. $LiNbO_3$ powder synthesized at $950^{\circ}C$ for 12 hours was found to be the best because it contains only the$LiNbO_3$ phase with the small particle size and uniform particle size distribution. As the sintering temperature and the soaking time increase, the sintered feed-rods exhibited the higher sintered density and grain growth phenomena. The $LiNbO_3$ feed rods sintering at $1100^{\circ}C$ for 2 hours were found to have the best microstructure for the precursor feed-rods of the floating zone crystal growth because of their higher density, small grain size and uniform particle size distribution. As the sintering temperature and the soaking time increase, the sintered feed-rods exhibited the higher sintered density and grain growth phenomena. The $LiNbO_3$ feed rods sintering at $1100^{\circ}C$ for 2 hours were found to have the best microstructure for the precursor feed-rods of the floating zone crystal growth because of their density, small grain size and uniform grain size distribution.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.577-582
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• 2015

The present study is concerned with the influence of niobium(Nb) addition and austenitizing temperature on the hardenability of low-carbon boron steels. The steel specimens were austenitized at different temperatures and cooled with different cooling rates using dilatometry; their microstructures and hardness were analyzed to estimate the hardenability. The addition of Nb hardly affected the transformation start and finish temperatures at lower austenitizing temperatures, whereas it significantly decreased the transformation finish temperature at higher austenitizing temperatures. This could be explained by the non-equilibrium segregation mechanism of boron atoms. When the Nb-added boron steel specimens were austenitized at higher temperatures, it is possible that Nb and carbon atoms present in the austenite phase retarded the diffusion of carbon towards the austenite grain boundaries during cooling due to the formation of NbC precipitate and Nb-C clusters, thus preventing the precipitation of $M_{23}(C,B)_6$ along the austenite grain boundaries and thereby improving the hardenability of the boron steels. As a result, because it considerably decreases the transformation finish temperature and prohibits the nucleation of proeutectoid ferrite even at the slow cooling rate of $3^{\circ}C/s$, irrespective of the austenitizing temperature, the addition of 0.05 wt.% Nb had nearly the same hardenability-enhancing effect as did the addition of 0.2 wt.% Mo.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.556-560
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• 2007

In this study, both structural and microwave dielectric properties of the $Mg_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1400^{\circ}C{\sim}1500^{\circ}C$. The bulk density and quality factor of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were increased with increasing sinterning temperature in the range of $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased the sintering temperature of above $1450^{\circ}C$. The dielectric constant of the $Mg_5Ta_4O_{15}$ ceramics was increased continuously with increasing sintering temperature. And the dielectric constant of the $Mg_5Nb_4O_{15}$ ceramics was increased in as the sintering temperature increasesfrom $1400^{\circ}C{\sim}1450^{\circ}C$ but was decreased at the temperatures above $1475^{\circ}C$. In the case of the $Mg_5Ta_4O_{15}\;and\;Mg_5Nb_4O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, $-10.91ppm/^{\circ}C$ and 14, 37,350 GHz, $-52.3ppm/^{\circ}C$, respectively.