Berlin 2015 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 52: Nanomaterials III: Nanoporous Gold and Phase Transformations
MM 52.5: Vortrag
Donnerstag, 19. März 2015, 12:45–13:00, H 0106
Molecular-dynamics simulation of martensite-austenite transition in nickel-titanium nanoparticles — •Christian Kexel1, Stefan Schramm1,2, and Andrey Solov'yov1,3 — 1Department of Physics, Goethe University, 60438 Frankfurt, Germany — 2Frankfurt Institute for Advanced Studies, Goethe University, 60438 Frankfurt, Germany — 3MBN Research Center, 60438 Frankfurt, Germany
Shape-memory alloys can after initial deformation reconstruct their pristine structure upon heating. The underlying phenomenon is the structural solid-solid transformation from low-temperature lower-symmetry martensite to high-temperature higher-symmetry austenite. The near-equiatomic NiTi possesses an eminent importance for biomedical applications whereas the nanostructured equivalent can exhibit yet enhanced thermomechanical properties. However, no plausible microscopic theory of the shape-memory effect in NiTi exists, especially for the nanoscale systems. In this work, the thermally-induced martensite-austenite transition in free nanocrystals with 8472 to 39349 atoms is investigated by means of classical molecular-dynamics simulations. Thereby a recently published study is complemented. Interatomic interactions are modeled by a semi-empirical many-body potential based on tight-binding second-moment approximation. The structural transition, revealing features of a first-order transformation, is successfully demonstrated and contrasted with melting, a quantum harmonic model and experimental findings. Moreover, a nucleation-growth process is observed as well as the irreversibility of the transition.