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MM: Fachverband Metall- und Materialphysik

MM 17: Poster Session

MM 17.61: Poster

Monday, March 26, 2012, 17:00–19:00, Poster B

Simulation of structural phase transitions and shape memory behavior in NiTi nanosystems — •Daniel Mutter and Peter Nielaba — Universität Konstanz, Fachbereich Physik, 78457 Konstanz

We present results of atomistic molecular dynamics simulations of structural phase transitions and shape memory behavior of NiTi nanosystems. The application of heating-cooling cycles to bulk systems (2000 atoms under periodic boundary conditions) confirmed the experimentally known strong dependence of B19'-to-B2 transition temperatures (TTs) on alloy composition, which could be related to an increasing lattice instability, arising when the perfect ordered composition with 50% Ni and 50% Ti is changed slightly [1]. By applying free boundary conditions, spherical NiTi nanoparticles are simulated, showing a size dependence of the TTs. Further calculations suggest this to be due to an increasing surface-to-volume fraction and therefore a major influence of the surface free energy when the system size is reduced [2]. In addition, the nanoparticles show twinning of differently orientated variants of a B19'-like structure at low temperatures. We apply loading-heating-cooling cycles to these systems, which shows a shape memory behavior at the nanoscale differing from the known bulk mechanism.

[1] D. Mutter and P. Nielaba, Phys. Rev. B 82, 224201 (2010).

[2] D. Mutter and P. Nielaba, Eur. Phys. J. B 84, 109 (2011).