Fatigue of wire+arc additive manufactured Ti-6Al-4V in presence of process-induced porosity defects

Emre Akgun, Xiang Zhang, Romali Biswal, Yanhui Zhang, Matthew Doré

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Currently, additive manufactured titanium alloy Ti-6Al-4V predominantly fails from process-induced defects, when subjected to cyclic loading in the polished condition. These defects not only lead to premature failure, but also contribute to the significant dispersion of fatigue life commonly seen in metal additive manufacturing. In this work, we have studied the source of dispersion and the influence of pore size on fatigue life using samples from the standard processing route and samples with intentionally introduced porosity defects. According to the fracture surface study, contrary to the common belief, the source of dispersion is primarily the pore location, e.g. surface or embedded pore, rather than the pore size. In the case of embedded pores as the failure source, a threshold pore size of approximately 85 μm was observed, below which the wrought level fatigue performance was achieved. For surface pores above the threshold size, fatigue life was reduced by two orders of magnitude, but remained unchanged, even though crack initiating pore size increased roughly by a factor of four. This experimental observation was supported by local elastic stress analysis, which indicated that pores above a certain size could behave like micro-notches suggesting the popular Kitagawa-Takahashi diagrams should be presented with a horizontal asymptote for this alloy.

    Original languageEnglish
    Article number106315
    Number of pages20
    JournalInternational Journal of Fatigue
    Volume150
    Early online date8 May 2021
    DOIs
    Publication statusPublished - Sep 2021

    Funder

    EPSRC

    Keywords

    • Additive manufacturing
    • Defects
    • Fatigue
    • Titanium
    • Wire+Arc additive manufacturing

    ASJC Scopus subject areas

    • Modelling and Simulation
    • Materials Science(all)
    • Mechanics of Materials
    • Mechanical Engineering
    • Industrial and Manufacturing Engineering

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