A new type of intrinsic two-way shape-memory effect in hooks of NiTi-wires

A. Schuster*, H. F. Voggenreiter, D. C. Dunand, G. Eggeler

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

8 Scopus citations

Abstract

Shape-memory hooks were fabricated in a single processing step ("one-time procedure") by a combination of tensile and bending deformation of a martensitic NiTi-wire. The hooks reversibly changed curvature on heating and cooling in a reproducible manner over 50 thermal cycles. This new type of intrinsic two-way shape memory effect was studied by subjecting the hooks to a beam of high-energy synchrotron x-rays at room temperature (<Mf) and at 150°C (>Af). This technique demonstrated that the hooks were martensitic at room temperature but contained both austenite and martensite at 150°C. The presence of martensite above Af is due to a high dislocation density, which stabilizes martensite and inhibits its transformation. The amount of stabilized martensite scales with the extent of plastic deformation and thus increases from the inner to the outer curvature of the hook. On heating, the inner part of the hook transforms to austenite, while the stabilized martensite in the outer part is deformed pseudo-elastically by twinning. On cooling, the back-transformation of the inner part is biased by the pseudo-elastic recovery of the outer part, thus forcing the hook back into its initial shape.

Original languageEnglish (US)
Pages (from-to)1177-1180
Number of pages4
JournalJournal De Physique. IV : JP
Volume112 II
DOIs
StatePublished - Oct 2003
EventInternational Conference on Martensitic Transformations - Espoo, Finland
Duration: Jun 10 2002Jun 14 2002

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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