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Effect of Milling Time Parameter on the Microstructure and the Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Alloys

Sharief P., Madavali B., Koo J. M., Kim H. J., Hong S., Hong S.-J.

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 2

585-590

EN

Nanostructured thermoelectric materials receiving great attention for its high thermoelectric performance. In this research, nanostructured n-type Bi2 Te2.7 Se0.3 alloys have prepared using high energy ball milling and followed by spark plasma sintering. Also, we have varied ball milling time to investigate milling time parameter on the thermoelectric properties of n-type Bi2 Te2.7 Se0.3 powder. The powders were discrete at 10 min milling and later particles tend to agglomerate at higher milling time due to cold welding. The bulk fracture surface display multi-scale grains where small grains intersperse in between large grains. The maximum Seebeck coefficient value was obtained at 20-min milling time due to their lower carrier density. The κ values were decreased with increasing milling time due to the decreasing trend observed in their κL values. The highest ZT of 0.7 at 350 K was observed for 30-min milling time which was ascribed to its lower thermal conductivity. The Vickers hardness values also greatly improved due to their fine microstructure.

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Influence of milling time on the mechanism of phase structure formation in mechanically alloyed Nd-Fe-B magnets.

Kaszuwara W., Leonowicz M.

Archives of Materials Science

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2004

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Vol. 25, nr 4

523-529

EN

Mechanical alloying is one of the major methods for the processing of nanocrystalline Nd-Fe-B alloys. Long-time milling of elementary powders leads to formation of phase structure consisting of nanocrystalline iron particles embedded in an amorphous matrix. Synthesis of the hard magnetic Nd2Fe14B phase occurs in the course of low-temperature diffusion anealing of the milled material. Milling time appears to be one of the crucial parameters, determining the final phase structure and the material properties. The DSC and Moessbauer spectroscopy studies showed that the milling time affects the mechanism of phase formation. The materials obtained with short milling times contain substantial amount of the Nd2Fe17 phase. One can conclude that the Nd2Fe14B phase is formed by transformation of the Nd2Fe17 phase accompanied by decomposition of the Fe2B phase. The degree to which the transformation occurs is controlled by the milling time. One can neither exclude the apperance of the liquid phase during annealing of the material within a short milling time. Keeping other processing parameters constant, the milling time also affects the microstructure of magnets, especially the distribution of the grain size. The mean grain size decreases substantially with extension of the milling time.

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Wpływ czasu mielenia na mikrostrukturę i skład fazowy magnesów Sm-Fe-N

Pawlik P., Wysłocki J. J., Pawlik K., Kaszuwara W., Leonowicz M.

Archiwum Nauki o Materiałach

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2002

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T. 23, nr 1

19-35

PL

Badano magnesy Sm-Fe-N wytworzone metodą dyfuzji reaktywnej. Stosując dyfrakcję rentgenowską i spektroskopię moessbauerowską stwierdzono, że badany magnes składa się z magnetycznie twardych faz: Sm2Fe17N0.86 i SmFe5 oraz fazy magnetycznie miękkiej alfa-Fe. Ponadto określono udziały objętościowe poszczególnych faz. Przeprowadzono obserwacje mikrostruktury z użyciem zarówno mikroskopu optycznego, jak i skaningowego mikroskopu elektronowego oraz transmisyjnego mikroskopu elektronowego. Zbadano również zmiany właściwości magnetycznych, takich jak: koercja, jHc, remanencja Mr i maksymalna gęstość energii magnetycznej (BH)max w zależności od czasu mielenia magnesów Sm-Fe-N.

EN

Permanent magnets Sm-Fe-N produced by reactive diffusion method were investigated. Using X-ray diffraction and Moessbauer spectroscopy it was found that this magnet consists of hard magnetic phases: Sm2Fe17N0.86 and SmFe5 and soft magnetic alpha-Fe phase. Furthermore, volume fractions of these phases were determined. The microstructure observations were performed using an optical metallographic microscope, a scanning electron microscope and a transmission electron microscope. Moreover, the changes in magnetic properties, such as coercive force jHc, remanence Mr and energy product (BH)max depending on grain size of the Sm-Fe-N magnet were reported.