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Impact of asymmetric martensite and austenite nucleation and growth behavior on the phase stability and hysteresis of freestanding shape-memory nanoparticles

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Ko,  Won-Seok
Adaptive Structural Materials (Simulation), Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
School of Materials Science and Engineering, University of Ulsan, 44610 Ulsan, Republic of Korea;

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Grabowski,  Blazej
Adaptive Structural Materials (Simulation), Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Neugebauer,  Jörg
Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Citation

Ko, W.-S., Grabowski, B., & Neugebauer, J. (2018). Impact of asymmetric martensite and austenite nucleation and growth behavior on the phase stability and hysteresis of freestanding shape-memory nanoparticles. Physical Review Materials, 2(3): 030601. doi:10.1103/PhysRevMaterials.2.030601.


Cite as: http://hdl.handle.net/21.11116/0000-0003-A2C2-A
Abstract
Martensitic transformations in nanoscaled shape-memory alloys exhibit characteristic features absent for the bulk counterparts. Detailed understanding is required for applications in micro- and nanoelectromechanical systems, and experimental limitations render atomistic simulation an important complementary approach. Using a recently developed, accurate potential we investigate the phase transformation in freestanding Ni-Ti shape-memory nanoparticles with molecular-dynamics simulations. The results confirm that the decrease in the transformation temperature with decreasing particle size is correlated with an overstabilization of the austenitic surface energy over the martensitic surface energy. However, a detailed atomistic analysis of the nucleation and growth behavior reveals an unexpected difference in the mechanisms determining the austenite finish and martensite start temperature. While the austenite finish temperature is directly affected by a contribution of the surface energy difference, the martensite start temperature is mostly affected by the transformation strain, contrary to general expectations. This insight not only explains the reduced transformation temperature but also the reduced thermal hysteresis in freestanding nanoparticles. © 2018 American Physical Society.