• 한국분말재료학회지
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• 제25권5호
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• pp.402-407
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• 2018

Molybdenum silicide has gained interest for high temperature structural applications. However, poor fracture toughness at room temperatures and low creep resistance at elevated temperatures have hindered its practical applications. This study uses a novel powder metallurgical approach applied to uniformly mixed molybdenum silicide-based composites with silicon carbide. The degree of powder mixing with different ball milling time is also demonstrated by Voronoi diagrams. Core-shell composite powder with Mo nanoparticles as the shell and ${\beta}-SiC$ as the core is prepared via chemical vapor transport. Using this prepared core-shell composite powder, the molybdenum silicide-based composites with uniformly dispersed ${\beta}-SiC$ are fabricated using pressureless sintering. The relative density of the specimens sintered at $1500^{\circ}C$ for 10 h is 97.1%, which is similar to pressure sintering owing to improved sinterability using Mo nanoparticles.

• 한국재료학회지
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• 제9권10호
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• pp.1018-1024
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• 1999

Sn-3.5Ag 무연합금을 Cu 및 Alloy42 리드프레임에 납땜접합 (solder joint)하고 미세조직, 젖음성, 전단강도, 시효효과를 측정하여 비교하였다. Cu의 경우, 땜납의 Sn기지상안에 Ag(sub)3Sn과 Cu(sub)6Sn(sub)5상이, 그리고 땜납/리드프레임의 경계면에서는 1∼2㎛ 두께의 Cu(sub)6Sn(sub)5상이 형성되었다. Alloy42의 경우, 기지상내에 있는 낮은 밀도의 Ag(sub)3Sn상만이, 그리고 계면에는 0.5∼1.5㎛ 두께의 FeSn(sub)2이 형성되었다. 한편, Cu에 비해 Alloy42 리드프레임에서 퍼짐면적은 크고 접촉각은 작아 더 우수한 젖음성을 나타내었으나, 전단강도는 35%, 연신율은 75%로 낮았다. 180℃에서 1주일간 시효처리 후, Cu 리드프레임에는 계면에 η-Cu(sub)6Sn(sub)5 층외에 ξ-Cu(sub)3Sn층이 성장하였고, Alloy42 리드프레임에는 기지상내에 Ag(sub)3Sn이 구형으로 조대하게 성장하였고, 계면에는 FeSn(sub)2층만이 약 1.5㎛로 성장하였다.

• 한국주조공학회지
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• 제20권5호
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• pp.323-329
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• 2000

The HSS consists of hard carbide and matrix of martensite, and so its characteristics of wear resistance, fracture resistance, and surface roughness are good. This study was undertaken to investigate the influence of Nb and V and manufacturing conditions on microstructural behaviors and characteristics in the HSS cylindrical specimens(90 $mm^{O.D.}$ ${\times}$ 60 $mm^{I.D.}$ ${\times}$ 50 $mm^H$) manufactured using VCC(Vertical Centrifugal Casting). In the specimen of Fe-2C-6Cr-1.5W-3Mo-4V alloy, the amount of MC carbide was increased and $M_7C_3$ carbide was decreased with the increase of V and Nb contents. The primary VC carbide was formed and followed by the rod-type eutectic MC carbide was formed in the cell boundary in 9%V added specimen. MC carbide was increased, and $M_7C_3$ carbide was decreased with the addition of Nb content. In the specimen containing more than 3%Nb, primary NbC carbide was formed within the cell of matrix. With increase in rpm, cell and carbides became fine, and amount of carbide $M_7C_3$ was decreased due to increase in cooling rate.

• 한국정밀공학회지
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• 제25권7호
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• pp.131-138
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• 2008

The microstructural effects on the ultrasonic nonlinearity were investigated in isothermally degraded ferritic 2.25Cr-1Mo steel and low cycle fatigued copper. The variation in ultrasonic nonlinearity (${\beta}/{\beta}_0$) was interpreted as resulting from microstructural changes supported by the electron microscopy and X-ray diffraction, in addition to the mechanical test (Victor's hardness and ductile-brittle transition temperature). The ultrasonic nonlinearity of 2.25Cr-1Mo steel increased abruptly in the initial 1,000 h of degradation, and then changed little due to the coarsening of carbide and precipitation of stable $M_6C$ carbide during isothermal degradation. The ultrasonic nonlinearity of copper increased with the fatigue cycles due to the evolution of dislocation cell substructure.

• 한국수소및신에너지학회논문집
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• 제30권1호
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• pp.1-7
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• 2019

The preparation and catalytic activities of various transition metal carbide crystallites (VC, MoC, WC) were examined in this study. In particular, the effect of different kinds of transition metal crystallites were scrutinized on the ammonia decomposition reaction. The experimental results showed that BET surface areas ranged from $8.3m^2/g$ to $36.3m^2/g$ and oxygen uptake values varied from $9.1{\mu}mol/g$ to $25.4{\mu}mol/g$. Amongst prepared transition metal carbide crystallites, tungsten compounds (WC) were observed to be most active for ammonia decomposition reaction. The main reason for these results were considered to be related to the extent of electronegativity between these materials. Most of transition metal carbide crystallites were exceeded by Pt/C crystallite. However, the steady state reactivities for some of transition metal carbide crystallites (WC) were comparable to or even higher than that determined for the Pt/C crystallite.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1998년도 특별강연 및 춘계학술발표 개요집
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• pp.257-259
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• 1998

• E2M - 전기 전자와 첨단 소재
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• 제22권2호
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• pp.25-32
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• 2009

• 열처리공학회지
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• 제13권6호
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• pp.412-419
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• 2000

There has been a considerable attention on Invar alloys due to its low thermal expansion property. A low thermal expansion property of Invar alloys, lower than $10^{-6}$ near the room temperature, is attractive for electric transmission lines and precision machine tools. However, the expansion property of Invar alloys is limited below about 520K, and mechanical properties are relatively low to apply to electric transmission line. In order to improve mechanical properties in this alloy, Ti alloying element was added to the $Ni_{38}-Mo_2-Cr_1-Fe$ invar alloy. The microstructure Ti added alloy showed finer than that of the unalloyed one. It was found that the (Mo, Ti), Mo carbide formed by Ti addition obstacled grain growth by pinning effect and supplyed recrystallization sites during heat-treatment. Optimum heat-treatment conditions with Ti addition were also discussed in the modified Invar alloy.

• 공업화학
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• 제20권1호
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• pp.28-33
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• 2009

카본나노튜브에 담지된 몰리브데늄 카바이드 촉매를 다양한 제조 조건을 통해 제조하여 촉매특성을 분석하였고, 메탄올의 전기화학적 산화반응을 통해 촉매의 활성을 비교하였다. 촉매로써 전이금속의 낮은 활성을 극복하기 위한 방안으로 카본나노튜브를 지지체로 사용하였으며 전구체의 양 및 종류, 지지체의 산처리 방법, 탄화공정 온도조건 등을 변화하여 촉매를 제조하였다. 제조된 촉매는 ICP-AES, XRD, TEM을 통하여 촉매의 특성을 분석하였고, 메탄올의 전기화학적 산화반응을 통해 촉매의 활성을 비교하였다. 몰리브데늄 카바이드 촉매($Mo_2C/CNT$)의 다양한 제조방법으로 입자크기와 담지량을 변화시킬 수 있었으며, 입자의 크기와 담지량의 변화에 따른 전기화학적 산화반응의 특성을 설명할 수 있었다.

• 동력기계공학회지
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• 제4권1호
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• pp.74-80
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• 2000

This present study was investigated effect of Ni contents on the high temperature strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restraint laves phase formation. Precipitation amount of carbide, number of particle per unit area and particle size of carbide were decreased with increase of Ni content. In the steels, carbides of $M_{23}C_6$ type was mainly precipitated, but laves phases could not precipitated. Tensile and yield strength, creep strength and creep rupture time was decreased, but elongation were increased due to decreasing of particle number per unite area and carbide amount precipitated with increase of Ni content.