Simulation of the thermally induced austenitic phase transition in NiTi nanoparticles |
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| Authors: | D Mutter P Nielaba |
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| Institution: | (1) Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093-0411, USA;(2) Department of Mechanical Engineering, San Diego State University, San Diego, CA 92182-1323, USA;(3) Departments of Mechanical and Aerospace Engineering and Nanoengineering, University of California, San Diego, La Jolla, CA 92093-0411, USA; |
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| Abstract: | The reverse martensitic (“austenitic”) transformation upon heating of equiatomic
nickel-titanium nanoparticles with diameters between 4 and 17 nm is analyzed by means of
molecular-dynamics simulations with a semi-empirical model potential. After constructing
an appropriate order parameter to distinguish locally between the monoclinic
B19′ at low and the cubic B2 structure at high temperatures, the process of
the phase transition is visualized. This shows a heterogeneous nucleation of austenite at
the surface of the particles, which propagates to the interior by plane sliding,
explaining a difference in austenite start and end temperatures. Their absolute values and
dependence on particle diameter are obtained and related to calculations of the surface
induced size dependence of the difference in free energy between austenite and martensite. |
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