Europhys. Lett.
Volume 71, Number 1, July 2005
Page(s) 98 - 103
Section Condensed matter: structural, mechanical and thermal properties
Published online 27 May 2005
Europhys. Lett., 71 (1), pp. 98-103 (2005)
DOI: 10.1209/epl/i2005-10061-y

Size-dependent martensitic transformation path causing atomic-scale twinning of nanocrystalline $\chem{NiTi}$ shape memory alloys

T. Waitz, D. Spisák, J. Hafner and H. P. Karnthaler

Institute of Materials Physics University of Vienna Boltzmanngasse 5, A-1090 Vienna, Austria

received 14 March 2005; accepted in final form 4 May 2005
published online 27 May 2005

Nanocrystalline $\chem{NiTi}$ alloys were processed by devitrification of an amorphous phase to elucidate the impact of the nanocrystallinity on the thermally induced martensitic phase transformation. Forced by a size-dependent strain energy barrier, atomic-scale twinning leads to a unique path of the martensitic phase transformation. The observed twin boundaries of very low energy facilitate arrays of compound twins on atomic scale to overcome the strain energy barrier of the nanograins thus violating the hitherto well-established theory of martensite formation.

64.70.Nd - Structural transitions in nanoscale materials.
68.35.-p - Solid surfaces and solid-solid interfaces: Structure and energetics.
68.37.Lp - Transmission electron microscopy (TEM) (including STEM, HRTEM, etc.).

© EDP Sciences 2005