Contributions of porosity and laser parameter drift to inter-build variation of mechanical properties in additively manufactured 316 L stainless steel

Brendan P. Croom*, Phillip Koshute, Edwin B. Gienger, Ian D. McCue, Christopher Peitsch, John Mark Mines, Samuel Price, Ryan Carter, Robert K. Mueller, Justin Rettaliata, Michael Presley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The tensile mechanical properties of metals manufactured by laser powder bed fusion (L-PBF) are known to vary systematically between builds, posing challenges for the qualification and adoption of L-PBF. In this work, we systematically investigated two mechanisms that have previously been used to explain systematic differences in mechanical behavior of notionally identical L-PBF samples between builds (so called “inter-build variation”): porosity and laser parameter drift. Over 250 tension coupons, each with unique laser processing parameters, were built in 316 L stainless steel across three L-PBF builds, screened using high-resolution X-ray Computed Tomography to quantify internal porosity, and then mechanically tested. Notionally identical samples from one build showed statistically significant differences in porosity (0.045%, vs. 0.001% for the “best” build), ultimate tensile strength (614 vs. 588 MPa), and elongation (0.267 vs. 0.321 strain to failure), revealing meaningful levels of inter-build variation. Statistical and machine-learning guided interrogation of the relationships between laser processing conditions, porosity and mechanical response showed that the both laser parameter drift and systematic differences in porosity can both adequately explain observations of inter-build variation, but their effects are nonlinear and are most relevant in different regimes of build quality. In the present case, laser parameter drift within high-density samples can result in material with improved strength and reduced ductility due to microstructural refinement; on the other hand, porosity above ∼0.1% that is caused by process drift or other means contributes to rapid embrittlement, as in (Boyce et al., 2017).

Original languageEnglish (US)
Article number117998
JournalJournal of Materials Processing Technology
Volume317
DOIs
StatePublished - Aug 2023

Funding

This material is based upon work funded by the Naval Sea Systems Command ( NAVSEA ) under contract N00024–13-D-6400 . This material has been marked Distribution Statement A, approved for public release, and distribution is unlimited.

Keywords

  • AM qualification
  • Laser-powder bed fusion
  • Mechanical properties
  • Stainless steel
  • X-ray computed tomography

ASJC Scopus subject areas

  • Ceramics and Composites
  • Computer Science Applications
  • Metals and Alloys
  • Industrial and Manufacturing Engineering

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