Superelastic NiTi Thin Films for Medical Applications
Shape memory alloys are able to provide high work output when due to the martensitic transformation. Therefore, they are a promising candidate for actuation mechanisms in microsystems, e.g. in microvalves. Sputter deposited SMA thin films are already in use as free-standing films or as composites. Since it is also possible to deposit and structure the SMA composites on Si substrates by photolithographic techniques, the fabrication process is compatible to MEMS and therefore most favorable for an number of applications. Superelastic shape memory materials are of special interest in medical applications due to the large strains at constant stress and their biocompatibility. Superelastic NiTi thin films have been fabricated by magnetron sputtering using cast melted targets. Special heat treatment was performed to adjust superelastic properties and transformation temperatures. A superelastic strain of up to 6.5% at 37°C was obtained. Although NiTi shows an excellent biocompatibility enhanced antibacterial properties would significantly broaden its application range. Coatings containing Ag have already been used for this application. In order to apply this approach to TiNi-based alloys thin films of different TiNiAg compositions have been prepared by sputtering.
Pietro VINCENZINI and Stefano BESSEGHINI
E. Quandt and C. Zamponi, "Superelastic NiTi Thin Films for Medical Applications", Advances in Science and Technology, Vol. 59, pp. 190-197, 2008