• 한국결정성장학회지
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• 제21권6호
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• pp.246-252
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• 2011

반도성 $MnSi_{1.73}$ 화합물은 고온 특성이 우수하고 뛰어난 내산화성을 가진 열전재료로서 알려져 있다. 본 연구에서는 순 Mn 및 Si 분말재료를 출발 원료로 기계적 합금화법(MA)을 적용하여 $MnSi_{1.73}$ 화합물 합성을 실시하였다. MA 처리는 P-5 유성형 볼밀장치를 이용하여 Ar 중에서 행하였다. MA 분말재료의 X선 회절, 열분석 및 전자현미경 분석을 통하여 고상반응을 관찰하였다. MA 공정 중 Si의 손실을 고려하여 화학양론 조성에서 Si 양을 증가시켜 $MnSi_{1.73}$ 화합물 합성을 시도하였다. 그 결과 $MnSi_{1.73}$ 화합물 단상은 $MnSi_{1.88}$ 조성의 혼합 분말을 200시간 볼밀 처리함으로써 얻을 수 있었다. 또한 200시간 볼밀 처리에 의하여 제조된 $MnSi_{1.73}$ 화합물의 평균결정립 크기는 40 nm 임을 X 선 회절피크의 Hall plot으로 부터 알 수 있었다.

• 한국재료학회지
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• 제14권11호
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• pp.802-806
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• 2004

Skutterudite $CoSb_3$ powders were produced by mechanical alloying (MA) of elemental powders using a nominal stoichiometric composition. Annealing of MA powders under specific condition led to a complete phase transformation to a semiconducting ${\delta}-CoSb_3$. Single phase $CoSb_3$ was successfully produced by vacuum hot pressing using MA powders without subsequent annealing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD and SEM. Thermoelectric properties as a function of temperature were evaluated for the hot pressed specimens and compared with results of analogous studies.

• 한국재료학회지
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• 제13권9호
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• pp.561-566
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• 2003

Mechanical alloying(MA) process using elemental powders followed by hot pressing has been applied to some intermetallic alloy system containing ferromagnetic elements, such as NiAl and $FeSi_2$. A modified thermogravimetric analysis (TGA) technique was used to investigate the degree of alloying in milled powders and hot consolidated specimens as well as heat-treated bulk specimens. It is shown that the measurement of Curie temperatures in MA intermetallic powders and consolidated specimens containing ferromagnetic components, when determined as a function of milling and heat treatment parameters, can give some insight into the progress and mechanism of alloying.

• 한국재료학회지
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• 제29권4호
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• pp.252-257
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• 2019

Fabrication of soft magnetic composite powders for the $Fe_2O_3-Ca$ system by mechanical alloying(MA) has been investigated at room temperature. It is found that soft magnetic composite powders in which CaO is dispersed in ${\alpha}-Fe$ matrix are obtained by MA of $Fe_2O_3$ with Ca for 5 hours. Changes in magnetization and coercivity also reflect the details of the solidstate reduction process of hematite by pure metal of Ca during MA. The saturation magnetization of MA powders increases with increasing MA time and reaches a maximum value of 65 emu/g after 7 hours of MA. The average grain size of ${\alpha}-Fe$ in MA powders, estimated by diffraction line-width, gradually decreases with increasing MA time and reaches 52 nm after 5 hours of MA. It can also be seen that the coercivity of the 5-hour MA sample is fairly high at 190 Oe, suggesting that the grain refinement of already-produced ${\alpha}-Fe$ tends to clearly occur during MA.

• 한국표면공학회지
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• 제27권4호
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• pp.215-222
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• 1994

The role dispersoids has been studied in a number of researches as a key point for the high strength application of dispersion strengthened aluminum alloy. The mechanical alloying(MA) process with high mechanical properties of dispersion strengthened MA Al-8Ti-1B alloys were invested in order to evaluate their stress corrosion cracking(SCC) application. SCC properties of the mechanically alloyed Al-8Ti-1B were studied using slow strain rate test(SSRT). In this study Al-8Ti-1B alloy were more susceptible to SCC in solutions of pH=2.01 and 13.2 than pH=6.81 solution. In this study Al-8Ti-1B alloys by MA had more SCC resistance than Al-8Ti alloys or Al 7075-T73 alloys. So Al-8Ti-1B alloys by MA had more resistance in SSRT SCC susceptinility test than any other above alloying metals.

• 한국분말재료학회지
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• 제11권3호
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• pp.247-252
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• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• 한국재료학회지
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• 제21권10호
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• pp.542-545
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• 2011

Half-Heusler alloys are a potential thermoelectric material for use in high-temperature applications. In an attempt to produce half-Heusler thermoelectric materials with fine microstructures, TiCoSb was synthesized by the mechanical alloying of stoichiometric elemental powder compositions and then consolidated by vacuum hot pressing. The phase transformations during the mechanical alloying and hot consolidation process were investigated using XRD and SEM. A single-phase, half- Heusler allow was successfully produced by the mechanical alloying process, but a minor portion of the second phase of the CoSb formation was observed after the vacuum hot pressing. The thermoelectric properties as a function of the temperature were evaluated for the hot-pressed specimens. The Seebeck coefficients in the test range showed negative values, representing n-type conductivity, and the absolute value was found to be relatively low due to the existence of the second phase. It is shown that the electrical conductivity is relatively high and that the thermal conductivities are compatibly low in MA TiCoSb. The maximum ZT value was found to be relatively low in the test temperature range, possibly due to the lower Seebeck coefficient. The Hall mobility value appeared to be quite low, leading to the lower value of Seebeck coefficient. Thus, it is likely that the single phase produced by mechanical alloying process will show much higher ZT values after an excess Ti addition. It is also believed that further property enhancement can be obtained if appropriate dopants are selectively introduced into this MA TiCoSb System.

• 한국분말재료학회지
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• 제8권2호
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• pp.104-109
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• 2001

The semiconducting ${\beta}-FeSi_2$ compound has been recognized as a thermoelectric material with excel-lent oxidation resistance and stable characteristics at elevated temperature. In the present work, we applied mechanical alloying(MA) technique to produce ${\beta}-FeSi_2$ compound using a mixture of elemental iron and silicon powders. The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The MA powders were characterized by the X-ray diffraction with Cu-K $\alpha$ radiation, thermal analysis and scanning electron microscopy. The single ${\beta}-FeSi_2$ phase has been obtained by mechanical alloying of $Fe_{33}Si_{67}$ mixture powders for 120 hrs or for 70 hrs coupled with the subsequent heat treatment up to $700^{\circ}C$. The grain size of ${\beta}-FeSi_2$ powders analyzed by Hall plot method was 44nm.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1316-1317
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• 2006

The paper investigates the possibility to avoid extrinsic embrittlement of $Ni_3Al$, also increasing the high temperature strength, by alloying with both Fe - of a high strengthening effect and Cr - able to remove a part of diffused oxygen along the grain boundaries. As Cr homogenization in $Ni_3Al$ is difficult because of its low diffusion coefficient, for its improving a mechanical alloying (MA) step before the compound synthesis by Self-propagating High-temperature Synthesis (SHS) was adopted. The obtained better homogenization resulted in higher mechanical resistance and deformability than of the unalloyed $Ni_3A/Ni_3Al$ alloys of the same composition obtained without MA step.

• 한국분말재료학회지
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• 제10권4호
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• pp.288-293
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• 2003

Mechanical alloying (MA) by high energy ball mill of Pure chromium Powders was carried out under the nitrogen gas atmosphere. Cr-N amorphous alloy powders have been produced through the solid-gas reaction subjected to MA. The atomic structure during amorphization process was observed by X-ray and neutron diffractions. An advantage of the neutron diffraction technique allows us to observe the local atomic structure surrounding a nitrogen atom. The coordination number of metal atoms around a N atom turns out to be 5.5 atoms. This implies that a nitrogen atom is located at both of centers of the tetrahedron and octahedron formed by metal atoms to stabilize an amorphous Cr-N structure. Also, we have revealed that a Cr-N amorphous alloy may produced from a mixture of pure Cr and Cr nitrides powders by solid-solid reaction during mechanical alloying.