Effect of deposition strategies on fatigue crack growth behaviour of wire + arc additive manufactured titanium alloy Ti–6Al–4V

Abdul Syed, Xiang Zhang, Alec Davis, Jacob Kennedy, Filomeno Martina, Jialuo Ding, Stewart Williams, Philip Prangnell

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    Abstract

    The influence of three deposition strategies on the fatigue crack growth behaviour of Wire + Arc Additive Manufactured (WAAM) Ti–6Al–4V has been investigated in the as-built condition. Test samples were prepared using single pass, parallel pass, and oscillation deposition strategies and tested with cracks propagating parallel and normal to the plane of deposition. Due to the higher local heat input, the oscillation build exhibited a significantly coarser columnar β grain structure as well as a coarser transformation microstructure, compared to the single pass and parallel pass builds, which were very similar. Among the three build methods, the lowest crack growth rates were found with the oscillation build. The crack growth data was found to broadly fall between that of a recrystallized α (mill-annealed) and β annealed wrought material, with the oscillation strategy build behaving more similarly to a β annealed microstructure. The fatigue crack growth rate was lower when cracks were propagated perpendicular to the build layers. For each build strategy, a greater microstructural influence on crack growth rate was found at lower levels of stress intensity factor range (<25 MPa m1/2). However, the anisotropy and scatter in the data was much more significant in the case of the oscillation build. These differences have been attributed to the stronger α microtexture heterogeneity present in the oscillation build, which led to a greater crack deflection and bifurcation, giving rise to lower crack growth rates and a higher sensitivity to the anisotropy caused by the directional β grain structure.
    Original languageEnglish
    Article number141194
    Number of pages12
    JournalMaterials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
    Volume814
    Early online date3 Apr 2021
    DOIs
    Publication statusPublished - 13 May 2021

    Bibliographical note

    This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

    Funder

    We would like to thank Barry Meek, Martyn Cockell and Steve Damms at Coventry University for their support during the sample machining. We also thank the UK Engineering and Physical Science Research Council ( EPSRC ) for supporting this research through the NEWAM programme grant ( EP/R027218/1 ). Professor P.B. Prangnell is grateful to the Royal Academy of Engineering , UK, and Airbus for financial support through the Airbus- University of Manchester Centre for Metallurgical Excellence. The authors are also appreciative of the EPSRC programme grant LightForm ( EP/R001715/1 )

    Keywords

    • Additive Manufacturing
    • WAAM
    • Fatigue crack growth rate
    • Crack deflection
    • Titanium alloys

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