• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권7호
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• pp.352-357
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• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% TiB$_2$ and using 61vo1.% SiC - 39vo1.% WC powders with the liquid forming additives of 12wt% $Al_2$O$_3$＋Y$_2$O$_3$ by pressureless annealing at 180$0^{\circ}C$ for 4 hours. Reactions between SiC and transition metal TiB$_2$, WC were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H), TiB$_2$ and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-TiB$_2$, and SiC(2H), WC and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-WC composites. $\beta$\$\longrightarrow$$\alpha$-SiC phase transformation was ocurred on the SiC-TiB$_2$, but $\alpha$\$\longrightarrow$$\beta$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the vicker's hardness, the flexural strength and the fracture toughness showed respectively value of 96.2%, 13.34GPa, 310.19Mpa and 5.53Mpaㆍml/2 in SiC-WC composites. The electrical resistivity of the SiC-TiB$_2$ and the SiC-WC composites is all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to 50$0^{\circ}C$. 2.64${\times}$10-2/$^{\circ}C$ of PTCR of SiC-WC was higher than 1.645${\times}$10-3/$^{\circ}C$ of SiC-TiB$_2$ composites.posites.

• Composites Research
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• 제33권4호
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• pp.185-190
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• 2020

티타늄은 우수한 생체 적합성으로 임플란트 재료로 많이 사용되고 있지만 높은 비용과 뼈 대비 높은 영률로 인한 문제점이 있다. 이를 대체할 재료로 마그네슘합금이 주목받고 있다. 마그네슘합금은 티타늄과 마찬가지로 생체 적합성이 우수하고 뼈와 비슷한 영률을 가지고 있다. 하지만 부식으로 인한 내식성 문제가 있어 이를 해결하기 위해 다양한 표면 처리법이 연구되고 있다. 본 연구는 EDTA를 포함한 전해 용액에서 AZ31 마그네슘 합금 표면에 전해플라즈마공정으로 세라믹 코팅 층을 성장시키고 형성된 코팅의 특성은 SEM, XRD를 통해 미세구조 및 형상을 분석하였고 코팅 층의 미세 경도 측정을 하였으며, 사람의 혈장과 비슷한 성분인 SBF용액 내에서 부식테스트를 통해 생체내에서의 부식 특성을 평가하였다.

• 한국기계가공학회지
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• 제16권6호
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• pp.87-94
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• 2017

Hot stamping processes are possible for tensile strength 1.4 GPa but the strength reduction is appeared from the cooling performance unbalance. And the strength of roll forming process is below than that of hot stamping process owing to using the steel which is lower strength of boron steel. In this study, We provide roll forming process asssisted high-frequency induction heating to solve the problem of conventional one. The experiments were carried out at under various sill side part conditions: high-frequency induction heating conditions of 15, 18, 21, 24, 27 and 30 kW. The high-frequency induction heating temperature was checked with Infrared camera and the sill side parts of mechanical properties and microstructure were measured. The heating temperature of high frequency induction was measured to max $850^{\circ}C$ under the coil power of 30 kW. The tensile strength was 1.5 GPa and hardness was 490 Hv. The martensite structure was discovered under coil power of 30 kW. The weight of steel material sill side having thickness 1.5 mm and the boron steel sill side having thickness 1.2 mm were compared to weight effect. The boron steel sill side reduced 11.5% compared to steel. Consequently, manufacturing process of 1.5 giga-grade's sill side part was successfully realized by the roll forming assisted high-frequency induction heating methods.

• Journal of Ginseng Research
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• 제19권1호
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• pp.62-72
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• 1995

During the controlled atmosphere storage (CA), fresh ginseng showed good appearance in quality, and other deterioration of freshness was not observed until 12 weeks. On the other hand, MA storage had kept freshness only in treatment of 1 until 8 weeks. There was no significant difference between treated and non-treated sample with preservatives, and not treated sample was not infected with various different fungi. Moisture contents and hardness of ginseng in all treatments were not changed much until 12 weeks, and surface shrinkage did not occur either. But shear stress increased somewhat in all treatments after 12 weeks. The granule of microstructure in tissue diminished slightly. The apparent Quality of red ginseng was good until 4 weeks of treatment. But as time passed, white skin and wrinkled skin were generated and darkened in its color. B-1 in CA and E-1 in MA were found to be the most favorable one. The content of crude saponin did not change significantly during storage of CA or MA by preservation conditions and period. Though a small increase in saponin content from 4.92% to 5.43% was recognized in B-1, which was treated with preservative and 6.0% In B-2, control, this could rather explain increment of soluble component by butanol. Thus, there was no change in total contents of ginsenoside pattern and composition of each content. The Rbl content in B-1 and B-2 were 0.98%, and 0.97%, respectively, whereas that of control was 0.96%. E-1 of MA, treated with preservative was 5.32% after 12 weeks, but was 5.73% in control, indicating that ginsenosides pattern was quite similar to that of CA storage.

• 한국재료학회지
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• 제8권10호
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• pp.938-944
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• 1998

$MoSi_2$에 W분말을 첨가하여 $MoSi_2$/W 복합재료를 $1600^{\circ}C$에서 3시간 동안 유지하면서 30MPa의 조건하에서 고온진공 가압기를 이용하여 제조하였으며, 텅스텐 분말의 첨가량이 $(Mo)Si_2$의 미세조직과 기계적 성질에 미치는 영향을 조사하였다. 텅스텐은 몰리브덴과 치환하면서 고용체 합금을 이루었으며, 입자의 크기는 텅스텐 분말의 첨가량이 증가할수록 감소하였다. 비커스경도는 텅스텐 분말의 첨가량이 증가할수록 향상되었으나, 반면에 압흔파단 강도는 오히려 감소되었다. 10%정도의 텅스텐 분말을 첨가하였을 때, 압흔파단 강도가 $4.5MPa$\sqrt{m}$로서 순수 $MoSi_2$의 $2.7MPa\sqrt{m}$에 비하여 향상되었음을 알 수 있었다.

• 한국산학기술학회논문지
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• 제16권9호
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• pp.5743-5747
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• 2015

본 연구에서는 가스아토마이저로 제조된 Fe계 벌크비정질 합금 분말을 이용하여 제작된 시험편에 레이저 육성용접을 하였고, 인장시험과 경도시험의 실시 및 미세조직을 관찰하여 육성용접 층의 파괴거동을 분석하였다. 인장시험 결과 육성용접층은 탄성변형 후 바로 파괴가 일어났고, 모재는 소성변형 후 파괴가 일어났다. 육성용접층과 모재의 실제 최대인장강도는 각 각 955.9Mpa과 220.4Mpa이다. 육성용접층과 모재의 미소경도는 각 각 $485.5{\pm}21$과 $197.4{\pm}14$ 이었고, 육성용접층은 매우 높은 경도를 갖는다. 모재는 조대한 결정립을 갖는 미세 구조를 나타내었다. 인장시험 후 파단면을 고분해능주사전자현미경으로 관찰한 결과 육성용접층과 모재의 파괴형태는 각각 취성파괴와 연성파괴를 나타내었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.124-125
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• 2007

The composites were fabricated $\beta$-SiC and $TiB_2$ powders with the liquid forming additives of 8, 12, 16[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressureless annealing at $1,650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. The relative density, the flexural strength, the Young's modulus and the Vicker's hardness showed the highest value of 82.29[%], 189.5[MPa], 54.60 [GPa] and 2.84[GPa] for SiC-$TiB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature. The relative density of SiC-$TiB_2$ composites was lowered due to gaseous products of the result of reaction between SiC and $Al_2O_3+Y_2O_3$. The electrical resistivity showed the lowest value of 0.012[${\Omega}{\cdot}cm$] for 16[wt%] at 25[$^{\circ}C$]. The electrical resistivity was all negative temperature coefficient resistance (NTCR) in the temperature ranges from 25[$^{\circ}C$] to 700[$^{\circ}C$].

• 한국진공학회지
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• 제4권S2호
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• pp.100-105
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• 1995

Nitrogen implantation process has been applied for improvement of wear resistance of Zircaloy-4 fuel cladding materials. Nitrogen was implanted at 120keV to a total dose range of $1\times 10^{17}$ions/$\textrm{cm}^2$ to $1\times 10^{18}$ions/$\textrm{cm}^2$ at various temperatures between $270^{\circ}C$ and $671^{\circ}C$. The microstructure changes by nitrogen implantation were analyzed by XRD and AES and wear behavior was evaluated by performing ball-on-disc type wear testing at various loads and sliding velocities under unlubricated condition. Nitrogen implantation produced ZrNx nitride above $3\times 10^{17}$ions/$\textrm{cm}^2$ as well as heavy dislocations, which resluted in an increase in microhardness of the implanted surface of up to 1400 $H_k$ from 200 $H_k$ of unimplanted substrate. Hardness was also found to be increased with increasing implantation temperature up to 1760 $H_k$ at $620^{\circ}C$. The wear resistance was greatly improved as total ion dose and implantation temperature increased. The effective enhancement of wear resistance at high dose and temperature is believed to be due to the significant hardening associated with high degree of precipitation of Zr nitrides and generation of prismatic dislocation loops.

• 한국진공학회지
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• 제4권S2호
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• pp.40-48
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• 1995

$TiB_2$-TiN double-layer coating have been prepared by ion beam enhanced deposition. AES, XRD, TEM and HRTEM were employed to characterize the $TiB_2$ layer. The microhardness of the coatings was evaluated by an ultra low-load microhardness indenter system, and the tribological behavior was examined by a ball-on-disc tribology wear tester. It was found that in a single titanium diboride layer, the composition is uniform along the depth of the film, and it is mainly composed of nanocrystalline $TiB_2$ with hexagonal structure, which resulted from the ion bombardment during the film growth. The hardness of the $TiB_2$ films increases with increasing ion energy, and approaches a maximum value of the $TiB_2$ films increases with increasing ion energy, and approaches a maximum value of 39 Gpa at ion energy of 85 keV. The tribological property of the TiB2 films is also improved by higher energy of 85keV. The tribological property of the $TiB_2$ films is also improved by higher energy ion beam bombardment. There is no major disparity in the mechanical properties of double-layer $TiB_2$/TiN coatings and TiN/$TiB_2$ coatings. Both show an improved wear resistance compared with single-layer $TiB_2$ films. The adhesion of double-layer coatings is also superior to that of single-layer films.

• Journal of Welding and Joining
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• 제27권6호
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• pp.17-24
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• 2009

The Friction Stir Welding(FSW) has mainly been used for making butt joints in Al alloys. Development of Friction Stir Lap Welding(FSLW) would expand the number of applications. Microstructure of FSLW in A5052-H112 alloy was investigated under varying rotation and welding speed. As the rotation speed was increased and the welding speed was decreased, a amount of heat was increased. As a result, bead interval was narrower, bead width are larger, and experimental bead interval was almost similar to theoretical bead interval. Typical microstructures of FSLW A5052-H112 alloy consist of three zones, including Stir Zone(SZ), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). As a amount of heat was increased, average grain size was larger in three zones. Nevertheless, the aspect ratio was almost fixed for FSLW conditions. The misorientation of SZ, HAZ and TMAZ was examined. A large number of low angle grain boundaries, which were formed by severe plastic deformation, were showed in TMAZ as comparison with SZ and HAZ. Microhardness distribution was high in order of BM, SZ, TMAZ, and HAZ. The Micro-hardness distribution in HAZ, TMAZ of upper plate were lager than lower plate. Relationship between average grain size and microhardness was almost corresponded to Hall-Petch equation.