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MM: Fachverband Metall- und Materialphysik

MM 31: Postersitzung II

MM 31.19: Poster

Mittwoch, 16. März 2011, 17:15–18:45, P5

Simulation of structural transitions in NiTi systems — •Daniel Mutter and Peter Nielaba — University of Konstanz, 78457 Konstanz, Germany

In this work, we performed atomistic molecular dynamics simulations of the structural phase transition in NiTi alloys between B19' at low and B2 at high temperatures [1]. To this end, a semi-empirical potential from the literature was adopted [2] and modified, which is based on the tight-binding model in second moment approximation. We present an analysis of crystallography and energetics of the emerging structures during a heating-cooling cycle, which is applied to systems with 2048 atoms under periodic boundary conditions. The experimentally known strong dependence of transition temperatures (TTs) on alloy composition is confirmed and related to an increasing lattice instability, arising when the perfect ordered composition with 50% Ni and 50% Ti is changed slightly. By applying free boundary conditions, spherical NiTi nanoparticles with diameters between 3 and 17 nanometers were simulated, where a size dependence of the TTs was observed. In order to explain this behavior, an order parameter for distinguishing locally between B19' and B2 was constructed, with which a visualization of the phase transition was possible, showing that the start of the structural transformation is mainly triggered by the surface of the nanoparticle.

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

[2] W.S. Lai, B.X. Liu, J. Phys. Cond. Mat. 12, L53-L60 (2000).