Blown-powder direct-energy-deposition of titanium-diboride-strengthened IN718 Ni-base superalloy

Riddhi Sarkar, Bo Chen, Michael E. Fitzpatrick, Tim Hilditch, Daniel Fabijanic

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Abstract

This paper reports on the adoption of TiB2 as an inoculant to fabricate IN718 via the direct energy deposition (DED) process. Effective grain refinement and low texture were achieved in IN718/TiB2 using a TiB2 powder size of d90 = 10 μm and mass fraction of 1.5 wt%. The use of low linear energy density (33.08 J/mm) produced IN718/TiB2 deposits free from large grains (>300 μm), however at the cost of the formation of interlayer defects. By comparison, the large grains were present in deposits made with a linear energy density of 78.74 J/mm and also in deposits manufactured without an included inoculant. Production of deposits at lower energies without interlayer defects was possible by reducing the powder flow rate to 7 g/min. However, this caused a moderate increase in grain size. The TiB2 inoculant reduced the Laves phase network by replacing it with homogeneously distributed Cr-, Mo-, Nb-, and B-enriched needle-shaped precipitates. Tensile strength increased by 300–500 MPa with TiB2 addition, but at the cost of significant ductility drop, regardless of the deposition conditions. The IN718 deposit displayed many micro-cracks at the network of Laves phase during tensile loading, whereas micro-cracks in the IN718/TiB2 occurred at the interface between the needle-shaped precipitates and the matrix. The strength enhancement in IN718/TiB2 was by a combination of strengthening mechanisms: grain boundary, dislocation structure formation, Orowan-type and load transfer related to the needle-shaped precipitates.

Original languageEnglish
Article number145617
Number of pages18
JournalMaterials Science and Engineering: A
Volume885
Early online date26 Aug 2023
DOIs
Publication statusPublished - 3 Oct 2023

Bibliographical note

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).

Funder

Bo Chen acknowledges the financial supports from the UK's Engineering and Physical Sciences Research Council, EPSRC Early Career Fellowship Scheme EP/R043973/1. MEF is grateful for the support of the Lloyd's Register Foundation, a charitable foundation helping to protect life and property by supporting engineering-related education, public engagement and the application of research.

Keywords

  • Direct energy deposition
  • Inconel 718
  • Microstructure
  • Inoculant
  • Tensile properties

ASJC Scopus subject areas

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

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