In-situ synthesis of oxides by reactive process atmospheres during L-PBF of stainless steel

• Published in: Additive manufacturing Vol. 33; no. C; p. 101178
• Main Authors: Haines, M.P., Peter, N.J., Babu, S.S., Jägle, E.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2020; Elsevier
• Subjects: Additive manufacturing; L-PBF; ODS alloys; Reactive process atmospheres; Stainless steel; ODS alloys; Reactive process atmospheres; Additive manufacturing; Stainless steel; L-PBF
• ISSN: 2214-8604; 2214-7810
• DOI: 10.1016/j.addma.2020.101178

[Display omitted] •Pyrometry showed an increase in intensity in CO2 atmosphere over Ar atmosphere.•At low levels of reactive gas atmospheres oxygen loss from spatter dominates.•Oxygen increased in samples from 0.016 wt.% in Ar to 0.1 wt.% in CO2.•Average in-situ particle size in the samples were ∼40 nm.•There was a 20 % increase in yield strength when samples were produced under CO2. Traditionally, reactive gases such as oxygen (O2) and carbon dioxide (CO2) have been avoided during laser powder bed fusion (L-PBF) of metals and alloys based on the notion that it may lead to defect formation and poor properties. Here we show that instead, these gases can be used to form sub-μm-sized oxide particles in-situ during the L-PBF process in an Fe-Cr-Al-Ti stainless steel and lead to improved room temperature and high-temperature mechanical properties. We manufactured cube samples using pure Ar and various reactive gas atmospheres, namely an O2/Argon (Ar) mixture containing 0.2 % O2 and CO2/Ar mixtures containing up to 100 % CO2. Co-axial measurements of infrared radiation emitted from the melt pool showed correlation to the presence of O2 or CO2 in the gas mixture. Builds produced under CO2-containing atmosphere contained complex oxides with an average diameter of ∼40 nm, an Al-rich core and a Ti-rich shell. Due to the high cooling rates typical to L-PBF, agglomeration of oxides and slag formation on the surface of the samples could almost be entirely avoided. Compression tests at temperatures up to 800 °C showed that the samples produced in 100 % CO2 have about 20 % higher yield stress compared to samples produced in Ar. The paper concludes with a discussion of the formation mechanism of the observed oxides. Our results show that in-situ reactions during additive manufacturing processes are a promising pathway to the synthesis of particle-reinforced alloys.