Understanding process atmosphere interactions in Electron Beam Powder Bed Fusion (EB-PBF) additive manufacturing
Typ
Examensarbete för masterexamen
Program
Materials engineering (MPAEM), MSc
Publicerad
2021
Författare
Burgman, Oskar
Lundberg, Christian
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The composition of the process atmosphere and its effect on the Ti-6Al-4V powder
during Electron Beam Melting with an Arcam Q20plus was studied. Oxygen concentration
and water vapour content were monitored in-situ in the build chamber and
in the gas exiting the chamber, using lambda sensors and a dew point meter. Composition
changes were analysed in the process atmosphere using mass spectrometry
and in Ti-6Al-4V powder, using X-ray photoelectron spectroscopy, Inert Gas Fusion
Analysis, and Scanning Electron Microscopy. Results show that the low supply of
oxygen introduced from the process atmosphere result in the moderate increase in
oxygen content, measured in the powder. The powder used had a high initial oxygen
concentration, which could also explain the low oxygen pick-up seen in the study. A
limited increase in oxide layer thickness can be observed on the studied powder, in
agreement with the moderate increase in general oxygen content. The powder morphology
and overall visual appearance studied in scanning electron microscopy also
remained unchanged. The study also shows that residual air and water are notable
constituents of the process atmosphere as the process starts. These constituents are
gradually replaced by helium during the first few hours of the manufacturing process,
while preheating occurs, where the oxygen content stabilises to a partial pressure
below 0.1 ppm in the process. This is within the limit of oxygen contained in the
helium. No significant variations in the oxygen content in the atmosphere between
builds was registered. The gas flow exiting the Q20plus proved to be insufficient
for the extractive lambda sensor and the dew point meter, rendering them unusable
for this specific process. The mass spectrometry results potentially indicate minor
air leaks into the vacuum chamber, as the relative amounts of nitrogen remain stable.
Beskrivning
Ämne/nyckelord
additive manufacturing , electron beam melting (EBM) , Ti-6Al-4V , powder , vacuum , oxygen uptake , mass-spectrometry , process gas monitoring