Strain and texture evolution during mechanical loading of a crack tip in martensitic shape-memory NiTi

M. R. Daymond*, M. L. Young, J. D. Almer, D. C. Dunand

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

88 Scopus citations

Abstract

In situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shape-memory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of NiTi. Upon subsequent application of a static tensile stresses, the highly textured zone reappears and grows around the crack tip as the applied stress is increased. At the highest applied stress intensity of 35 MPa m1/2, large tensile strains are measured ahead of the crack tip and considerable elastic anisotropy is observed. This detwinning zone is similar to the plastic zone produced by dislocation slip present around cracks in other metals. The texture in this zone is not significantly altered after mechanical unloading, despite the development of substantial triaxial compressive residual strains in this zone.

Original languageEnglish (US)
Pages (from-to)3929-3942
Number of pages14
JournalActa Materialia
Volume55
Issue number11
DOIs
StatePublished - Jun 2007

Keywords

  • Ni-Ti
  • Nitinol
  • Shape memory
  • Smart materials
  • Superelasticity

ASJC Scopus subject areas

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

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