Berlin 2005 – scientific programme
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DS: Dünne Schichten
DS 17: Harte Schichten und mechanische Eigenschaften
DS 17.3: Talk
Monday, March 7, 2005, 14:30–14:45, TU HS110
Probing superelasticity in NiTi-based shape memory thin films and foils – an advanced experimental approach — •R. Hassdorf1, J. Feydt1, S. Thienhaus1, L. Buforn2, N. Conté2, O. Pykhteev1, M. Kružík1,3, N. Botkin1, and M. Moske1 — 1Forschungszentrum caesar, 53175 Bonn, Germany — 2CSM Instruments SA, 2034 Peseux, Switzerland — 3Academy of Sciences, 182 08 Prague, Czech Republic
With the advent of functional vapor-deposited thin films, the incorporation of shape memory and superelastic materials into coatings and lithographically processed microstructures has gained high prospects and technological importance. This holds specifically for their use in medical devices and thermal actuators. However, with shrinking size scale, characterization of the nonlinear superelastic behavior has become more and more demanding. In this respect, we present a study demonstrating the use of different advanced characterization techniques. One of them is nanoindentation with spherical tipped indenters tested on MBE-grown submicron NiTiCu alloy thin films. By applying Hertzian contact mechanics, the full range of mechanical response can be obtained from elastic, through the yield point, to permanent deformation. Moreover, using an analytical approach the indentation data can be converted into a stress-strain scenario aimed at simulating uniaxial tension load. Therefrom, for the above mentioned films, the width of the superelastic region is determined to be around 3% strain which complies with finite-element simulations used to fit the indentation curves.
Supported by BMBF under contract no. 03N4031A.