• 한국분말재료학회지
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• 제10권1호
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• pp.46-50
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• 2003

Lee et al. reported that a mixture of Cu and Ta, the combination of which is characterized by a positive heat of mixing, $\{Delta}H_{mix}$ of +2 kJ/㏖, can be amorphized by mechanical alloying(MA). It is our aim to investigate to what extent the MA is capable of producing a non-equilibrium phase with increasing the heat of mixing. The system chosen is the binary $Cu_{30}Mo_{70}$ with $\{Delta}H_{mix}$=+19 kJ/㏖. The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The vial and balls are made of Cu containing 1.8-2.0 wt.%Be to avoid contaminations arising mainly from Fe when steel balls and vial are used. The MA powders were characterized by the X-ray diffraction, EXAFS and thermal analysis. We conclude that two phase mixture of nanocrystalline fcc-Cu and bcc-Mo with grain size of 10 nm is formed by the ball-milling for a 3:7 mixture of pure Cu and Mo, the evidence for which has been deduced from the thermodynamic and structural analysis based on the DSC, X-ray diffraction and EXAFS spectra.

• 한국분말재료학회지
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• 제12권6호
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• pp.433-440
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• 2005

The hydrogen sorption speed of $Zr_{57}V_{36}Fe_7$ nanocrystalline and amorphous alloys was evaluated at room temperature. Nanocrystalline alloys of $Zr_{57}V_{36}Fe_7$ were prepared by planetary ball milling. The hydrogen sorption speed of nanocrystalline alloys was higher than that of the amorphous alloy. The enhanced sorption speed of nanocrystalline alloys was explained in terms of surface oxygen stability which has been known to retard the activation of amorphous alloys. The retardation can be reduced by formation of nanocrystals, which results in the observed increase in sorption properties.

• 대한기계학회논문집A
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• 제33권4호
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• pp.440-446
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• 2009

This paper was designed to fabricate the miniature spur gear with pitch circle of 2.25mm using extrusion process of a mechanically alloyed Al-78wt%Zn powder. The mechanical alloying of the powder particles were performed for ball milled times of 4h, 8h, 16 and 32h by the planetary ball milling. The mechanical properties of these alloyed powders, which were compacted and sintered-cylindrical preforms, were estimated using compression test. The results showed that the alloyed powder with average particle size of $10{\mu}m$ milled for 32h has the highest compressive(fractured) strength(288MPa). Extrusions of the miniature spur gear using the alloyed powder were carried out at different extrusion temperatures. Extrusion temperature of $300^{\circ}C$ provided the spur gear with the highest relative density and Vickers hardness and without any surface defects.

• 한국분말재료학회지
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• 제12권3호
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• pp.174-178
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• 2005

This paper deals with the fabrication of titanium carbide using fine titanium hydride. The ratio of $TiH_2$ and C (Activated carbon) was 1:1 (mol) and milled in a planetary ball mill at a ball-to-powder weight ratio of 20:1. Thereafter, TGA was performed at $1400^{\circ}C$ to observe change of weight with milling time. Titanium carbide was obtained by using tempering the milled powders at $1100-1500^{\circ}C$. The microstructures of titanium carbide as well as the change of the lattice parameters and particle size have been studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

• 한국분말재료학회지
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• 제17권2호
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• pp.136-141
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• 2010

Bismuth-telluride based $(Bi_{0.2}Sb_{0.8})_2Te_3$ thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging $400\;nm\;{\sim}\;2\;{\mu}m$. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at $350^{\circ}C$ for 10 min at the heating rate of $100^{\circ}C/min$ and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity ($0.8\;m{\Omega}{\cdot}cm$) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.

• 전기학회논문지
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• 제66권11호
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• pp.1600-1604
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• 2017

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile and many other applications due to their excellent physical and electronic properties. Especially, Mo-Cu composites with 5~20 wt% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength and prominent electrical and thermal conductivity. In most of the applications, high dense Mo-Cu materials with homogeneous microstructure are required for high performance, which has led in turn to attempts to prepare ultra-fine and well-dispersed Mo-Cu powders in different ways, such as spray drying and reduction process, electroless plating technique, mechanical alloying process and gelatification-reduction process. However, most of these methods were accomplished at high temperature (typically degree), resulting in undesirable growth of large Cu phases; furthermore, these methods usually require complicated experimental facilities and procedure. In this study, Mo-Cu alloying were prepared by planetary ball milling (PBM) and spark plasma sintering (SPS) and the effect of Cu with contents of 5~20 wt% on the microstructure and properties of Mo-Cu alloy has been investigated.

• 대한금속재료학회지
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• 제50권10호
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• pp.769-774
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• 2012

Mg-x wt% $Fe_2O_3-y$ wt% Ni samples were prepared by reactive mechanical grinding in a planetary ball mill, and their hydrogen-storage properties were investigated and compared. Activations of $Mg-5Fe_2O_3-5Ni$ was completed after one hydriding (under 12 bar $H_2$) - dehydriding (in vacuum) cycle at 593 K. At n = 2, $Mg-5Fe_2O_3-5Ni$ absorbed 3.43 wt% H for 5 min, 3.57 wt% H for 10 min, 3.76 wt% H for 20 min, and 3.98 wt% H for 60 min. Activated $Mg-10Fe_2O_3$ had the highest hydriding rate, absorbing 2.99 wt% H for 2.5 min, 4.86 wt% H for 10 min, and 5.54 wt% H for 60 min at 593 K under 12 bar $H_2$. Activated $Mg-10Fe_2O_3-5Ni$ had the highest dehydriding rate, desorbing 1.31 wt% H for 10 min, 2.91 wt% H for 30 min, and 3.83 wt% H for 60 min at 593 K under 1.0 bar $H_2$.

• 한국재료학회지
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• 제21권7호
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• pp.384-390
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• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• Korean Chemical Engineering Research
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• 제54권1호
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• pp.44-51
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• 2016

전도성 물질인 철 입자(iron particles)를 절연체로 코팅하여 제작한 압분자심(powder core)은 비저항이 작기 때문에 고주파 영역에서 와전류 손실이 크다. 이 결함을 해결하기 위해서는 압분자심의 비저항을 증가시킬 필요가 있다. 이 연구에서는 압분자심의 비저항을 증가시키기 위하여 유성볼밀을 사용하여 전기전도성 철 입자에 산화제2구리를 코팅하였다. 반응표면분석법을 사용하여 코팅변수를 최적화하였다. 최적화 시 인자는 CuO 질량분율, 밀 회전 수, 코팅시간, 볼 크기, 볼 질량, 시료 질량이며, 반응변수는 비저항이었다. 6인자-일부요인배치법에 의하면 주된 인자는 CuO 질량분율, 밀 회전 수, 코팅시간이었다. 3-인자 완전요인배치법과 최대경사법을 사용하여 3개 인자의 수준을 선정하였다. 최대경사법을 사용하여 최고의 비저항을 갖는 영역에 접근하였다. 최종적으로 Box-Behnken법을 사용하여 스크린한 인자들의 반응표면을 분석하였다. Box-Behnken법 결과에 의하면 CuO 질량분율과 밀 회전 수가 코팅공정 효율에 영향을 주는 주요 인자이었다. CuO 질량분율이 증가함에 따라 비저항은 증가하였다. 그에 반해서 밀 회전 수가 감소함에 따라 비저항은 증가하였다. 코팅공정을 최적화한 모델로부터 계산한 예측값과 실험값과는 통계적으로 유의하게 일치하였다($Adj-R^2=0.944$). 비저항의 최고값을 갖는 코팅조건은 CuO 질량분율은 0.4, 밀 회전 수는 200 rpm, 코팅시간은 15분이었다. 이 조건에서 코팅한 정제의 비저항 측정값은 $530k{\Omega}{\cdot}cm$이었다.

• 한국수소및신에너지학회논문집
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• 제10권1호
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• pp.27-40
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• 1999

Mg 및 Ni chips을 사용하여 $Mg_2NiH_x$ 수소저장합금을 Planetary Ball Mill M/C로 제조하였으며, 합금화 과정 중에 미치는 분위기 수소압의 영향을 고찰하였다. XRD분석결과 1:30의 장입비에서는 24시간 합성조건일 경우 10 bar이상의 분위기에서 $Mg_2NiH_x$ 상이 발견되었으며 48시간 합성할 경우에는 5 bar 이상의 분위기에서 나타났다. 1:66의 장입 조건에서는 24, 48시간 모두 5 bar 이상의 분위기에서 $Mg_2NiH_x$ 가 검출되었다. 합금화 초기에 만들어지는 것으로 생각되는 $MgH_x$ 로 인하여 전 공정에 걸쳐 미반응 Ni가 잔류하였으며 TG 분석결과 합금화 과정 중에 흡수된 수소저장량은 수소압의 변화에 따라 1.1 ~ 3.9 wt%에 이르는 것으로 나타났다. SEM 관찰 결과 동일 공정 조건에서는 분위기 수소압의 증가가 합금화 결과 최종적으로 얻어지는 미세입자와 그 군집체의 형상 및 크기 변화에 큰 영향을 미치지 못하는 것으로 나타났다.