Hydrogen embrittlement behavior induced by dynamic martensite transformation of Ni-Ti superelastic alloy

Ken'ichi Yokoyama, Miho Tomita, Jun'ichi Sakai

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    Abstract

    The hydrogen embrittlement behavior induced by the martensite transformation of Ni-Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the martensite transformation steeply decreases with increasing number of deformation cycles, whereas the critical stress for the reverse transformation only slightly changes. The dynamic stress-induced martensite transformation markedly enhances hydrogen absorption, compared with that of the martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm; nevertheless, no fracture associated with the stress-induced martensite transformation occurs. In addition, no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally desorbed at a low temperature markedly increases, indicating that the hydrogen states are changed by the dynamic martensite transformation. Note that interactions between hydrogen and the phase transformation are probably irreversible, although the phase transformation is reversible. The present study shows, for the first time, that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the martensite transformation.

    Original languageEnglish
    Pages (from-to)1875-1885
    Number of pages11
    JournalActa Materialia
    Volume57
    Issue number6
    DOIs
    Publication statusPublished - 2009 Apr

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    Keywords

    • Hydrogen embrittlement
    • Martensite transformation
    • Ni-Ti
    • Shape memory alloy
    • Superelastic alloy

    ASJC Scopus subject areas

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

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