Size-dependent martensitic transformation path causing atomic-scale twinning of nanocrystalline shape memory alloys

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

Corresponding author: waitz@ap.univie.ac.at

Received: 14 March 2005
Accepted: 4 May 2005

Abstract

Nanocrystalline 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.