Surface chemistry in Ti-6Al-4V feedstock as influenced by powder reuse in electron beam additive manufacturing

X-ray photoelectron spectroscopy (XPS) as well as scanning and transmission electron microscopy (SEM/TEM) analysis was carried out on four Ti-6Al-4V powders used in electron beam powder-bed fusion (PBF-EB) production environments: virgin low oxygen (0.080 wt% O), reused medium oxygen (0.140 wt% O), reused high oxygen (0.186 wt% O), and virgin high oxygen (0.180 wt% O). The two objectives of this comparative analyses were to (1) investigate high oxygen containing Grade 23 Ti-6Al-4V powders which were further oxidized as a function of reuse and (2) comparing the two virgin Grade 23 and Grade 5 powders of similar oxygen content. The microstructure of the low oxygen virgin Grade 23 powder was consistent with martensitic alpha ' microstructure, whereas the reused powder displayed tempered alpha/beta Widm & auml;nstatten microstructure. XPS revealed a decrease in TiO2 at the surface of the reused powders with an increase in Al2O3. This trend is energetically favorable at the temperatures and pressures in PBF-EB machines, and it is consistent with the thermodynamics of Al(2)O(3 )vs. TiO2 reactions. An unexpected amount of nitrogen was measured on the titanium powder, with a general increase in nitride on the surface of the particles as a function of reuse in the Grade 23 powder.1

Automated summary

XPS and SEM/TEM analysis were conducted on Ti-6Al-4V powders with different oxygen contents to investigate the effects of reuse on powder characteristics. The results showed a decrease in TiO2 and an increase in Al2O3 on the surface of reused powders, which is consistent with thermodynamics. Additionally, a higher amount of nitrogen and nitride was found on the surface of Grade 23 powders as a function of reuse.