Effects of Hydrogen Charging on the Phase Transformation of Martensitic NiTi Shape Memory Alloy Wires

Yoav Snir, Matthew Carl, Nathan A. Ley, Marcus L. Young

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Ti-rich martensitic NiTi shape memory alloy (SMA) wires of 0.5 mm diameter were tested under hydrogen-charging conditions to reveal the effects on phase transformation. Hydrogen charging was performed by immersion testing for several durations. The SMA wires were characterized by differential scanning calorimetry (DSC), scanning electron microscopy with energy dispersive spectroscopy, and synchrotron radiation X-ray diffraction (SR-XRD) for the the as-received, polished, and hydrogen-charged conditions. The DSC revealed the phase-transformation behavior of the NiTi SMA wires. Single and triple heating/cooling cycles in the DSC show the relationship between hydrogen and temperature on the material. Five distinct peaks (peaks I–V) are observed during heating/cooling in the DSC. Peak I corresponds to the martensite-to-austenite (M → A) transformation. Peaks II, III, and IV are related to hydrogen charging. Peak II appears at about 210–230 °C, while peaks III and IV appear at about 350 and 440 °C, respectively. These higher temperature peaks, peaks II–IV, were observed for the first time for a martensitic NiTi SMA due to the large temperature range covered using the DSC. Only one peak (peak V) appears during cooling and corresponds to the austenite-to-martensite transformation peak. Ex situ and in situ SR-XRD revealed the phases and the crystallographic relationship to peaks I–V in the DSC.

Original languageEnglish
Pages (from-to)443-456
Number of pages14
JournalShape Memory and Superelasticity
Volume3
Issue number4
DOIs
StatePublished - 1 Dec 2017

Keywords

  • Cyclic stability
  • Enthalpy of transformation
  • Lattice correspondence
  • Martensite
  • Mechanical behavior
  • NiTi < materials
  • Shape memory

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials

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