Abstract
A unique microstructural feature often referred to as “fish-scale” has been reported in 316L austenitic stainless steel parts made by laser powder bed fusion (L-PBF) technique. Because the final microstructure is predominantly austenitic, with a face-centered cubic (γ-fcc) crystal structure, the “fish-scale” structures were originally assumed to be based on etching response due to crystallographic orientations of the solidified γ grains. This research evaluated this assumption through multi-length scale and site-specific characterization using optical microscopy, hardness mapping, X-ray diffraction, electron back-scattered diffraction imaging, and scanning transmission electron microscopy. The nanoscale compositional measurements suggest that the “fish-scale” structures are related to a phase selection phenomenon that occurs during solidification due to spatial and temporal variation of thermal gradients and liquid–solid interface velocity. This phenomenon triggers the transition from γ-fcc to body-centered cubic (bcc) δ-ferrite solidification and then subsequent solid-state phase transformations of this bcc to fcc at low temperature. The significance of these phase transformation pathways with reference to deployment of additively manufactured 316 stainless steel components for harsh environments relevant to power generation is discussed. Graphical Abstract: This research elucidated the mechanism for the “fish-scale” microstructure evolution in 316L additively manufactured stainless steel builds based on phase selection—either body- or fcc solidification—as a function of spatially varying thermal gradient and liquid–solid interface velocity within a single melt pool based on multi-length scale characterization and computational modeling.[Figure not available: see fulltext.]
| Original language | English |
|---|---|
| Pages (from-to) | 3321-3340 |
| Number of pages | 20 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 53 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 2022 |
| Externally published | Yes |
Funding
This research was supported by the Transformational Challenge Reactor Program supported by the US Department of Energy, Office of Nuclear Energy. Authors also acknowledge partial support from the US Department of Energy Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. We acknowledge the discussions and feedback of Dr. Alex Plotkowski on the interface response function models. S. S. Babu’s contribution to this research is partially supported by the US Department of the Navy Office of Naval Research under ONR Award Number N00014-18-1-2794. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Office of Naval Research. This manuscript has been authored by UT-Battelle, LLC, under Contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This research was supported by the Transformational Challenge Reactor Program supported by the US Department of Energy, Office of Nuclear Energy. Authors also acknowledge partial support from the US Department of Energy Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. We acknowledge the discussions and feedback of Dr. Alex Plotkowski on the interface response function models. S. S. Babu’s contribution to this research is partially supported by the US Department of the Navy Office of Naval Research under ONR Award Number N00014-18-1-2794. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Office of Naval Research. This manuscript has been authored by UT-Battelle, LLC, under Contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan ). On behalf of all authors, the corresponding author states that there is no conflict of interest.
