High-temperature functional behavior of single crystal Ni51.2Ti23.4Hf25.4 shape memory alloy

L. Patriarca, H. Sehitoglu, E. Yu Panchenko, Y. I. Chumlyakov

Research output: Contribution to journalArticlepeer-review

Abstract

In this work the functional behavior of the new Ni51.2Ti23.4Hf25.4 high temperature shape memory alloy is investigated along three crystal orientations in compression and compared with the polycrystal behavior. Transformation temperatures were measured following specific aging treatments with the aim to optimize the shape memory and pseudoelastic behaviors. Two aging treatments were then selected in order to fulfill the optimum pseudoelastic behavior (500°C/4 h), and the maximum transformation temperatures (550°C/10 h) without compromising the alloy functionality. High temperature X-ray diffraction was utilized to determine the crystal orientations in the austenite phase for the single crystal specimens. The martensite structure was found to be the B19 orthorhombic, in contrast with monoclinic structure for lower Hf contents. Digital image correlation was successively used during isobaric strain-temperature experiments on the single crystal and polycrystal specimens. Large strain heterogeneities were found for the single crystals which pair with X-ray diffraction data that show un-transformed austenite below the martensite finish temperature. This reveals the heterogeneity of the austenite-to-martensite transformation for the present NiTiHf alloy which explains the divergence between the theoretical and experimental transformation strains. In addition, using digital image correlation it is possible to capture the local strain fields associated with fully transformed specimen regions. The transformation strains calculated locally are in close agreement with the theoretical transformation strains calculated with lattice deformation theory for the cubic austenite to the orthorhombic martensite phase transformation.

Original languageEnglish (US)
Pages (from-to)333-343
Number of pages11
JournalActa Materialia
Volume106
DOIs
StatePublished - Mar 1 2016

Keywords

  • Digital image correlation
  • Shape memory alloy
  • Single crystals
  • Transformation strain
  • X-ray diffraction

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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