2018-Sustainable Industrial Processing Summit
SIPS2018 Volume 5. Zehetbauer Intl. Symp. / SISAM

Editors:	F. Kongoli, S. Kobe, M. Calin, J.-M. Dubois, T. Turna
Publisher:	Flogen Star OUTREACH
Publication Year:	2018
Pages:	154 pages
ISBN:	978-1-987820-90-4
ISSN:	2291-1227 (Metals and Materials Processing in a Clean Environment Series)

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Severe Plastic Deformation via High Pressure Torsion in Thermoelectrics

Gerda Rogl¹; Peter Rogl²; Ernst Bauer³; Michael J. Zehetbauer⁴;
¹CHRISTIAN DOPPLER LABORATORY FOR THERMOELECTRICITY, Wien, Austria; ²UNIVERSITY OF VIENNA, FACULTY OF CHEMISTRY, Wien, Austria; ³TECHNISCHE UNIVERSITäT WIEN, Vienna, Austria; ⁴UNIVERSITY OF VIENNA, Wien, Austria;
Type of Paper: Invited
Id Paper: 188
Topic: 42

Abstract:

Thermoelectric materials are able to directly convert thermal energy into electrical energy, and vice versa. The potential of a material for thermoelectric applications is determined by the dimensionless figure of merit, ZT, which is directly proportional to the Seebeck coefficient squared and the temperature, and inversely proportional to the electrical resistivity and thermal conductivity, the latter consisting of an electronic and phonon part. As the Seebeck coefficient, the resistivity and electronic part of the thermal conductivity, are interdependent, one way to enhance ZT is to reduce the phonon part by enhancing the scattering of the heat carrying phonons.
High pressure torsion (HPT) is known as an outstanding technique in the methods of severe plastic deformation (SPD) to produce bulk ultra fine grained and nano crystalline materials, by introducing many grain boundaries as well as defects like dislocations and point defects [1,2,3].
In the first step, HPT-mediated nano crystallization was used to reduce the thermal conductivity of ball milled (BM) and hot pressed (HP) skutterudites. The samples, which were HPT processed after BM and HP, show enhanced ZT values up to a factor of 2 in comparison to BM and HP samples.
In the second step, HPT at elevated temperatures and in argon atmosphere was used to directly consolidate skutterudite powders into a solid. This way, time and energy consuming BM and HP can be avoided [4,5].
In this paper, we compare the grain sizes as well as dislocation densities and structural, physical, and mechanical properties of BM + HP samples with BM + HP + HPT samples, along with HPT produced samples (synchrotron diffraction data, collected from 300 - 800 K, SEM and TEM investigations reveal the modifications).

Keywords:

Advanced materials; Electronic structures; Energy applications;


References:

[1] M.J. Zehetbauer, Y.T. Zhu (eds), Modeling of Strength and Strain Hardening of Bulk Nanostructured Materials in: Bulk nanostructured materials, Wiley VCH, Weinheim (2009).
[2] M. Zehetbauer, H.P. Stuewe, A. Vorhauer, E. Schafler, J. Kohut, Adv. Eng. Mater. 5 (2003) 33.
[3] T. Ungar, M. Zehetbauer, Scr. Mater. 35 (1996) 1467.
[4] G. Rogl, P. Rogl, E. Bauer, M. Zehetbauer, Severe plastic deformation, a tool to enhance thermoelectric performance, in: Thermoelectric Nanomaterials, K. Kuomoto, T. Mori (eds), Springer Series in Materials Science 182, Springer Verlag Berlin (2013).
[5] G. Rogl, A. Grytsiv, J. Bursik, J. Horky, R. Anbalagan, E. Bauer, R.C. Mallik, P. Rogl, M. Zehetbauer, Phys. Chem. Chem. Phys. 17 (2015) 3715.

Cite this article as:

Rogl G, Rogl P, Bauer E, Zehetbauer M. (2018). Severe Plastic Deformation via High Pressure Torsion in Thermoelectrics. In F. Kongoli, S. Kobe, M. Calin, J.-M. Dubois, T. Turna (Eds.), Sustainable Industrial Processing Summit SIPS2018 Volume 5. Zehetbauer Intl. Symp. / SISAM (pp. 123-124). Montreal, Canada: FLOGEN Star Outreach