Oral Presentation 26th ACMM “2020 Visions in Microscopy”

Direct observation of martensitic phase throughout build of additively manufacturing Ti-6Al-4V via electron beam melting (#5)

William Davids 1 2 , Hansheng Chen 1 2 , Andrew Breen 1 2 , Sophie Primig 3 , Xiaozhou Liao 1 , Sudarsanam S Babu 4 5 , Simon P Ringer 1 2
  1. School of Aerospace, Mechanical and Mechatronic Engineering , The University of Sydney , Glebe, NSW, Australia
  2. Australian Centre for Microscopy and Microanalysis , The University of Sydney , Glebe, NSW, Australia
  3. School of Materials Science and Engineering, UNSW , Sydney, NSW, Australia
  4. Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee , Knoxville, Tennessee, USA
  5. Manufacturing Demonstration Facility, Oak Ridge National Laboratory, Knoxville, Tennessee, USA

The aerospace industry demands strong, lightweight components of complex geometries for a variety of applications. Titanium alloys, e.g. Ti-6Al-4V, exhibit exceptional strength-to-weight ratio and corrosion resistance and are hence a top candidate for alloy selection. The recent emergence of additive manufacturing (AM) has mitigated the geometric constraints associated with more traditional casting methods and is already being used as a cost-effective solution for the manufacturing of complex parts, yet a better understanding of how build parameters influence the resulting microstructure is still required.

Steep thermal gradients and rapid cooling rates associated with laser-based AM lead to the formation of a completely martensitic microstructure [1-3] in Ti-6Al-4V. The resultant ductility is well below that required for critical structural applications [4]. Generally, electron beam melting (EBM) has allowed the formation of non-martensitic microstructures, namely an α+ β basket-wave structure, restoring ductility due to the intrinsic heat treatment associated with this process. However, martensite (α’) was reported in Ti-

Here, we report the direct observation of the martensitic alpha prime phase throughout EBM builds using a combination of microanalytical techniques including atom probe tomography (APT), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). Furthermore, alpha prime is shown to exist in builds larger in size, and therefore thermal mass, than that previously reported [5]. The findings provide valuable insights into the phase transformation behaviour during the rapid cooling and heating regimes of EBM.

 

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