Issue |
ESOMAT 2009
2009
|
|
---|---|---|
Article Number | 02022 | |
Number of page(s) | 8 | |
Section | Principles, Simulations, Materials: Background | |
DOI | https://doi.org/10.1051/esomat/200902022 | |
Published online | 01 September 2009 |
DOI: 10.1051/esomat/200902022
On the influence of crystal defects on the functional stability of NiTi based shape memory alloys
Burkhard Maass, Juri Burow, Jan Frenzel and Gunther EggelerInstitute of Materials, Ruhr University Bochum, 44801 Bochum, Germany
burkhard.maass@rub.de
Published online: 1 September 2009
Abstract
The cyclic application of the shape memory effect in NiTi based shape memory alloys is
associated with a degradation of the functional properties. In the present work, we show how the
functional stability of NiTi based shape memory alloys depends on various microstructural defects
like grain boundaries, dislocations and substitutional elements (Fe replacing Ni). As a general
trend, it was observed that thermal cycling results in a decrease in phase transformation
temperatures. Nano-grained microstructures provide a significantly higher functional stability
than coarse grained microstructures due to reduced dislocation activity. Cold work impedes phase
transformation processes and provides a slight improvement of the functional stability. Fe
additions to NiTi are associated with the occurance of two-step transformations (cooling: B2 ⇒ R ⇒ B19’, heating: B19’ ⇒ R ⇒ B2) which allow partial thermal cycling (B2 ⇔ R and R ⇔
B19’). We show that B2 ⇔ R cycling has a better stability than R ⇔ B19’ cycling due to a
better crystallographic compatibility between B2 and R.
© Owned by the authors, published by EDP Sciences 2009