An investigation into the laser-based powder bed fusion process for Ti6Al4V components

Student thesis: Doctoral Thesis

Abstract

There is a requirement for a more in-depth understanding into the relationship between the process parameters and the powdered feedstock used during the manufacture of Ti6Al4V components via the Laser-based Powder Bed Fusion (L-PBF) process. It is particularly important to monitor the quality of titanium alloy powder during a top-up recycle regime. As the repeated exposure to the processing conditions can lead to powder property variation occurring. In addition, a more comprehensive assessment of spatter particles, generated during laser-powder interaction, is required.

This research will aim to investigate (i) the quality of ELI Ti6Al4V powder throughout a top-up recycling regime, (ii) the effect of recycling powder and hatch spacing parameter has on part properties, (iii) the characterisation of spatter particles captured during sieving, (iv) the influence that the energy density parameter has on mechanical properties of titanium alloy components produced by the L-PBF process.

ELI Ti6Al4V (Grade 23) powder was subjected to 9 recycle iterations. A full, comprehensive assessment of the powder was performed at each cycle, from the virgin state. The effect that recycled powder and the hatch spacing parameter, ranging from 0.1 mm to 0.06 mm, had on the hardness of the as-built components was quantified via statistics. The particle shape, size and chemistry of spatter formed at recycle 7 was analysed and compared with plasma-atomised (PA) virgin powder. A process parameter variation was performed to correlate the energy density with the quality of the Ti6Al4V components, relative to their hardness, density and nature of porosity present.

The oxygen content reached the maximum limit (0.13 wt.%) for the ELI grade after 8 recycles. The oxygen levels within the spatter particles exceeded both the maximum limit for the Grade 5 (0.2 wt. %) and Grade 23 (0.13 wt. %)Ti6Al4V alloys. It was statistically proven, via a regression analysis, that the hatch spacing parameter had a significant effect on the hardness.
Date of AwardFeb 2022
Original languageEnglish
SupervisorShaun Mc Fadden (Supervisor) & Justin Quinn (Supervisor)

Keywords

  • Additive manufacturing
  • Titanium alloy
  • Selective laser melting

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