Deformation of lamellar γ-TiAl below the general yield stress

Thomas Edward James Edwards, Fabio Di Gioacchino, Amy Jane Goodfellow, Gaurav Mohanty, Juri Wehrs, Johann Michler, William John Clegg

    Research output: Contribution to journalArticleScientificpeer-review

    13 Citations (Scopus)


    The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64% of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.) lamellar interfaces of all types in soft mode-oriented colonies. These stretched the full colony width and the shear strain was most intense in the centre of the colonies. Further, the most highly operative microbands of plasticity at specimen fracture were not those most active prior to yielding. The strain mapping results from polycrystalline tensile loading were further compared to those from microcompression testing of soft-mode stacks of lamellae milled from single colonies performed at the same temperatures. Combined with post-mortem transmission electron microscopy of the pillars, the initial plasticity by longitudinal dislocation glide was found to locate within 30–50 nm of the lamellar interfaces, and not at the interfaces themselves. The highly localised plasticity that precedes high cycle fatigue failure is therefore inherently related to the lamellar structure, which predetermines the locations of plastic strain accumulation, even in a single loading cycle.

    Original languageEnglish
    Pages (from-to)122-139
    Number of pages18
    JournalActa Materialia
    Early online date2018
    Publication statusPublished - 15 Jan 2019
    Publication typeA1 Journal article-refereed


    • Deformation twinning
    • Digital image correlation
    • Electron backscattering diffraction (EBSD)
    • Pre-yield plasticity
    • Titanium aluminide

    Publication forum classification

    • Publication forum level 3

    ASJC Scopus subject areas

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


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