• Journal of Powder Materials
• /
• v.8 no.2
• /
• pp.104-109
• /
• 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.

• Korean Journal of Materials Research
• /
• v.14 no.11
• /
• pp.802-806
• /
• 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.

• Journal of Powder Materials
• /
• v.1 no.2
• /
• pp.167-173
• /
• 1994

Cu-10wt%W composite powders have been manufactured by a high energy ball milling technique. The composite powders were pressed at 250 MPa and sintered in a dry hydrogen at 103$0^{\circ}C$ for 4 hours. After sintering, Cu-10wt%W composite materials were forged. And the arc-resistance of forged materials which have the same relative density of 94% has been tested. Composite particles, i.e. tungsten particles distributed homogeneously in the copper matrix, was formed after 480 min mechanical alloying. Densities of these sintered materials were ranged from 74 to 84%. Densification degree was due to the formation of composite powders. As the mechanical alloying time increased, the hardness was increased and tungsten particle size was decreased. Arc loss of the forged specimens was decreased as increasing the mechanical alloying time.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1316-1317
• /
• 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.

• Journal of Powder Materials
• /
• v.3 no.1
• /
• pp.33-41
• /
• 1996

Nanostructured Cu-Pb powders were synthesized by mechanical alloying process. The variation of powder characteristics with mechanical alloying time was investigated by x-ray diffraction, differential scanning calorimetry, SEM and TEM. An electrical resistivity of the hot pressed specimens was also measured by using the nanovoltmeter. It was shown that mechanical alloying for 12 hours leads to a homogenization and a grain refinement to the nanometer scale under 20 nm. The mechanically alloyed Cu-Pb alloys represented the enhanced solid solubility of 10wt% Pb in the Cu matrix. The monotectic temperature of nanostructured Cu-Pb alloy decreased from equilibrium state of 955$^{\circ}C$ to 855$^{\circ}C$ due to reduced grain size effect. The analysis of electrical resistivity showed that the hot pressed MA Cu-5wt% Pb compact existed as a solid solution.

• Journal of Powder Materials
• /
• v.18 no.5
• /
• pp.401-405
• /
• 2011

Half-heusler phase ZrNiSn is one of the potential thermoelectric materials for high temperature application. In an attempt to investigate the effect of Sb doping on thermoelectric properties, half-heusler phase $ZrNiSn_{1-x}Sb_x$ ($0{\leq}x{\leq}0.08$) was synthesized by mechanical alloying of stoichiometric elemental powder compositions, and consolidated by vacuum hot pressing. Phase transformations during mechanical alloying and hot consolidation were investigated using XRD. Sb doped ZrNiSn was successfully produced in all doping ranges by vacuum hot pressing using as-milled powders without subsequent annealing. Thermoelectric properties as functions of temperature and Sb contents were evaluated for the hot pressed specimens. Sb doping up to x=0.04 in $ZrNiSn_{1-x}Sb_x$ was shown to be effective on thermoelectric properties and the figure of merit (ZT) was shown to reach to the maximum at x=0.02 in this study.

• Journal of Powder Materials
• /
• v.10 no.4
• /
• pp.288-293
• /
• 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.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1997.11a
• /
• pp.70-71
• /
• 1997

• Korean Journal of Materials Research
• /
• v.11 no.12
• /
• pp.1020-1027
• /
• 2001

Powder type Ag system insert metals were manufactured by mechanical alloying method. Alloying method was the ball milling process using zirconia ball media, and all alloying variables were constant except the milling time. The milling times were selected 24, 48 and 72 hours. The insert metals made by milling method were observed using scanning electron microscope and x-ray analyses. And also, the evaluation of wettability and microstructures of the insert metals were conducted to investigate the characteristics of the brazed joint. The wettability of the insert metals made by milling of 48 hours, was the best condition. And the insert metals contained Cd shows good wettability, however, there was the oxides residue on the brazing test specimen. The microstructures of the manufactured and the commercial insert metals were almost same displaying the Cu- rich proeutectic and Ag-rich eutectic. Further, there were some porosities. The 48 hours alloyed insert metal was exhibited the most sound brazed joint without containing porosity due to the superior wettability and good alloying condition.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.6
• /
• pp.246-252
• /
• 2011

The semiconducting $MnSi_{1.73}$ compound has been recognized as a thermoelectric material with excellent oxidation resistance and stable characteristics at elevated temperature. In the present work, we applied mechanical alloying (MA) technique to produce $MnSi_{1.73}$ compound using a mixture of elemental manganese 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. Due to the observed larger loss of Si relative to Mn during mechanical alloying of $MnSi_{1.73}$, the starting composition of a mixture Mn-Si was modified to $MnSi_{1.83}$ and then $MnSi_{1.88}$. The single $MnSi_{1.73}$ phase has been obtained by mechanical alloying of $MnSi_{1.88}$ mixture powders for 200 hours. It is also found that the grain size of $MnSi_{1.73}$ compound powders analyzed by Hall plot method is reduced to 40 nm after 200 hours of milling.