• Wilson, Robert
• Delooze, Geoff
• Nguyen, Vu
• Yang, Kun

Abstract

Ti-6Al-4V alloy picks up interstitial elements easily when being manufactured by laser-based additive manufacturing (LBAM), leading to increased yield strength but reduced ductility. This research studies the directed-energy deposition (DED) of Ti-6Al-4V alloy in an argon atmosphere containing 9 to 9500ppm oxygen (from air), using both fresh and recycled feedstock powders. It is found that yield strength and ultimate tensile strength increase and the elongation to fracture decrease with oxygen exposure. When exposed to 3500ppm oxygen containing atmosphere, an oxygen pickup of 1000ppm and a nitrogen pickup of 600ppm is identified for samples built using fresh feedstock powders. However, a yield strength of 1061±0.6MPa and an elongation to fracture of 10.5±1.6% are still obtained. The resulting microstructure for all the samples with oxygen exposure comprises full lamellar α+β, formed through the in-situ decomposition of martensite and/or massive α phase. The α lath thickness is found to increase with oxygen exposure level due to the increased β-transus temperature and martensite start temperature. Oxygen pickup tends to saturate but nitrogen pickup keeps increasing for the air exposure level range investigated. When exposed to argon atmospheres containing similar levels of oxygen, the recycled powder builds are stronger but less ductile than the fresh powder builds. This is due to the smaller average particle sizes of the recycled powders and their larger specific surface area from the DED process, which result in a higher pickup of interstitial elements with no saturation for the air exposure level investigated.

Topics

• Deposition
• impedance spectroscopy
• microstructure
• surface
• phase
• Oxygen
• reactive
• laser emission spectroscopy
• Nitrogen
• strength
• yield strength
• tensile strength
• interstitial
• ductility
• decomposition
• directed energy deposition