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

Journal Article · Mon Aug 16 00:00:00 EDT 2004 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.1783011· OSTI ID:20632726

Lee, Hoo-Jeong; Ramirez, Ainissa G ^[1]

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1. Department of Mechanical Engineering, Yale University, New Haven, Connecticut 06520 (United States)

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{sup '} structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470 deg. C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35 deg. C. Calorimetric measurements are consistent with the observed crystallization.

• OSTI ID: 20632726
• Journal Information: Applied Physics Letters, Vol. 85, Issue 7; Other Information: DOI: 10.1063/1.1783011; (c) 2004 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AMORPHOUS STATE
ANNEALING
AUSTENITE
CALORIMETRY
COOLING
CRYSTALLIZATION
DEPOSITION
ELECTRONS
GRAIN GROWTH
HEATING
MARTENSITE
MEMBRANES
MICROSTRUCTURE
MONOCLINIC LATTICES
NICKEL ALLOYS
SHAPE MEMORY EFFECT
SILICON NITRIDES
THIN FILMS
TITANIUM ALLOYS
TRANSMISSION ELECTRON MICROSCOPY