NiTi and NiTi-TiC composites: Part IV. Neutron diffraction study of twinning and shape-memory recovery

D. C. Dunand*, D. Mari, M. A M Bourke, J. A. Roberts

*Corresponding author for this work

Research output: Contribution to journalArticle

79 Scopus citations

Abstract

Neutron diffraction measurements of internal elastic strains and crystallographic orientation were performed during compressive deformation of martensitic NiTi containing 0 vol pet and 20 vol pet TiC particles. For bulk NiTi, some twinning takes place upon initial loading below the apparent yield stress, resulting in a low apparent Young's modulus; for reinforced NiTi, the elastic mismatch from the stiff particles enhances this effect. However, elastic load transfer between matrix and reinforcement takes place above and below the composite apparent yield stress, in good agreement with continuum mechanics predictions. Macroscopic plastic deformation occurs by matrix twinning, whereby (1 0 0) planes tend to align perpendicular to the stress axis. The elastic TiC particles do not alter the overall twinning behavior, indicating that the mismatch stresses associated with NiTi plastic deformation are fully relaxed by localized twinning at the interface between the matrix and the reinforcement. For both bulk and reinforced NiTi, partial reverse twinning takes place upon unloading, as indicated by a Bauschinger effect followed by rubberlike behavior, resulting in very low residual stresses in the unloaded condition. Shape-memory heat treatment leads to further recovery of the preferred orientation and very low residual stresses, as a result of self-accommodation during the phase transformations. It is concluded that, except for elastic load transfer, the thermal, transformation, and plastic mismatches resulting from the TiC particles are efficiently canceled by matrix twinning, in contrast to metal matrix composites deforming by slip.

Original languageEnglish (US)
Pages (from-to)2820-2836
Number of pages17
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume27
Issue number9
DOIs
StatePublished - Jan 1 1996

ASJC Scopus subject areas

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

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