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Transformation properties and microstructure of sputter-deposited Ni-Ti shape memory alloy thin films

Lehnert, T. ; Crevoiserat, S. ; Gotthardt, R.

In: Journal of Materials Science, 2002, vol. 37, no. 8, p. 1523-1533

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    Title
    • Transformation properties and microstructure of sputter-deposited Ni-Ti shape memory alloy thin films
    Author
    • Lehnert, T.. Institut de Physique de la Matiére Complexe, Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
    • Crevoiserat, S.. Institut de Physique de la Matiére Complexe, Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
    • Gotthardt, R.. Institut de Physique de la Matiére Complexe, Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Journal of Materials Science, 2002, vol. 37, no. 8, p. 1523-1533. Kluwer Academic Publishers
    Other Version
    Classification
    • Engineering
    OAI-PMH Identifier
    • oai:doc.rero.ch:319875
    Summary
    The influence of annealing parameters on the martensitic phase transformation in sputter-deposited Ti rich Ni-Ti films is systematically studied by differential scanning calorimetry and by transmission electron microscopy. The annealing temperature range extends from the crystallization temperature of the films up to 900°C. For increasing temperature, multiple phase transformations, transformations via an R-phase or direct martensite/austenite transformations are observed. A similar behavior is found for increasing annealing time. Related changes of the film microstructure, such as the strongly varying distribution of round Ti2Ni precipitates in the grains, are analyzed. Transformation temperatures could be shifted over a wide range by adjusting the film composition from 48 to 54 at.% Ti. The corresponding transformation curves, grain structure as well as nature and amount of precipitates were investigated. No subsequent annealing process is required for films deposited on substrates heated above about 500°C. In this case, the as-deposited films have a very fine-grained and homogeneous microstructure