Use of electrical resistance testing to redefine the transformation kinetics and phase diagram for shape-memory alloys

Z. He*, K. R. Gall, L. C. Brinson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

The phase-transformation temperatures of a nickel-titanium-based shape-memory alloy (SMA) were initially evaluated under stress-free conditions by the differential scanning calorimetric (DSC) technique. Results show that the phase-transformation temperature is significantly higher for the transition from detwinned martensite to austenite than for that from twinned martensite (or R phase) to austenite. To further examine transformation temperatures as a function of initial state, a tensile-test apparatus with in-situ electrical resistance (ER) measurements was used to evaluate the transformation properties of SMAs at a variety of stress levels and initial compositions. The results show that stress has a significant influence on the transformation of detwinned martensite, but a small influence on the R-phase and twinned martensite transformations. The ER changes linearly with strain during the transformations from both kinds of martensite to austenite. The linearity between the ER and strain during the transformation from detwinned martensite to austenite is not affected by the stress, facilitating application to control algorithms. A revised phase diagram is drawn to express these results.

Original languageEnglish (US)
Pages (from-to)579-587
Number of pages9
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume37
Issue number3
DOIs
StatePublished - Mar 2006

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

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