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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Bulk Nanocrystalline Shape Memory Alloys Processed by Severe Plastic Deformation
Thomas Waitz1;1UNIVERSITY OF VIENNA, FACULTY OF PHYSICS, PHYSICS OF NANOSTRUCTURED MATERIALS, Vienna, Austria;
Type of Paper: Regular
Id Paper: 235
Topic: 42
Abstract:
Bulk ultrafine-grained, nanocrystalline, and even amorphous materials can be processed using methods of severe plastic deformation (SPD). [1,2] The small grain size as well as the high density of defects can significantly impact the phase stability and thus the physical properties of various materials. Control of phase stability by methods of SPD is of special interest in the case of functional materials such as shape memory alloys. [3] Their unique thermomechanical properties are based on a martensitic phase transformation that can be strongly affected by lattice defects, chemical disordering, and a grain size at the nanoscale. In the present work, examples of SPD processed shape memory alloys include Ni-Ti, low-hysteresis Ti-Ni-Pd, high temperature Ti-Pd and Ti-Pt, as well as ferromagnetic Ni-Mn-Ga. Their phase stability and the martensitic morphology in the small grains were systematically investigated using methods of transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction, including in-situ heating, cooling, and straining experiments carried out in the synchrotron. With decreasing grain size, the martensitic transformation is hindered and metastable adaptive martensitic phases might occur. However, the thermally and stress induced transformations might be suppressed completely in grains smaller than a corresponding critical value. Considering a size dependent energy barrier opposing the transformation and the mechanisms of self-triggered autocatalytic interactions of the transformation in neighbouring grains, the results were modelled using the general thermodynamic framework of martensite formation. [4]
Keywords:
Advanced materials; Atomic structures; Surfaces and interfaces;References:
[1] R.Z.Valiev, Y. Estrin, Z. Horita, T.G. Langdon, M.J. Zehetbauer, Y.T. Zhu, JOM 58 (2006) 33-39.[2] R.Z.Valiev, Y. Estrin, Z. Horita, T.G. Langdon, M.J. Zehetbauer, Y.T. Zhu, JOM 68 (2016) 1216-1226.
[3] T. Waitz, W. Schranz, A. Tröster, Springer Series in Materials Science 198 (2014) 23-56.
[4] M. Petersmann, T. Antretter, T. Waitz, F.D. Fischer, Modelling Simul. Mater. Sci. Eng.
25 (2017) 035004