A critical evaluation of the microstructural gradient along the build direction in electron beam melted Ti-6Al-4V alloy

Hitesh Sharma, David Parfitt, Abdul Syed, David Wimpenny, Emmanuel Muzangaza, Gavin Baxter, Bo Chen

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    24 Citations (Scopus)
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    Abstract

    It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Here we present an unambiguous evaluation of this microstructural gradient and associated mechanical property along the EBM build direction on purpose-built round bar RB samples with build height of 380 mm and rectangular plate RP samples with build height of 120 mm. Columnar prior β grain width was found to increase (from 86±38 to 154±56 μm in RB and from 79±34 to 122±56 μm in RP samples) with the build height and the similar increase was also observed for α lath width (from 0.58±24 to 0.87±33 μm in RB and from 1.50±45 to 1.80±49 μm in RP samples). These observations can be attributed to the thermal gradient in the powder bed that produced a cooling rate gradient along the build height. The measured α lath width variation along the build height followed a lognormal distribution. The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean α lath width by following a Hall-Petch relation.
    Original languageEnglish
    Pages (from-to)182-194
    Number of pages13
    JournalMaterials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
    Volume744
    Early online date5 Dec 2018
    DOIs
    Publication statusPublished - 28 Jan 2019

    Bibliographical note

    NOTICE: this is the author’s version of a work that was accepted for publication in Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 744, (2019) DOI: 10.1016/j.msea.2018.12.016

    © 2018, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/

    Keywords

    • Additive manufacturing
    • Electron beam melting
    • Graded microstructure
    • Mechanical property
    • Titanium

    ASJC Scopus subject areas

    • Materials Science(all)
    • Condensed Matter Physics
    • Mechanics of Materials
    • Mechanical Engineering

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