TITLE

Crystallization and phase transformations in amorphous NiTi thin films for microelectromechanical systems

AUTHOR(S)
Hoo-Jeong Lee; Ramirez, Ainissa G.
PUB. DATE
August 2004
SOURCE
Applied Physics Letters;8/16/2004, Vol. 85 Issue 7, p1146
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Amorphous sputtered nickel–titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (cubic B2 structure) with heating; and the conversion of austenite (B2) to martensite (monoclinic B19′ structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470°C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35°C. Calorimetric measurements are consistent with the observed crystallization.
ACCESSION #
14085047

 

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