Synergistic Effects of Defects and Microstructure on Mechanical Behavior of LB-LBF Metallic Materials

The overarching goal of the proposed research is to enable prediction of mechanical properties of additively manufactured (AM) metallic materials by considering the characteristics of defects and their surrounding microstructure. To achieve this goal, this project investigates the synergistic effects of defects and their surrounding microstructure on the mechanical properties of laser beam powder bed fused (LB-PBF) metallic materials, including IN718 and SS 316L. This research ad-dresses the main hindrance of adopting AM metallic materials in flight critical applications, i.e., their compromised and hard-to-predict mechanical behavior due to the presence of volumetric defects, including pores (gas-entrapped pores and key holes) and lack-of-fusions. Indeed, the mechanical performance (such as fatigue resistance and high strain rate response) is associated with significant scatter due to the stochastic nature of these defects and their surrounding microstructure. The central objectives of this research are to: (1) Assess the effects of defect size/shape and microstructure on the fatigue behavior of AM IN718, (2) Based on the fatigue data on AM IN718, incorporate the synergistic effects of defects and microstructure on fatigue performance into a predictive model, (3) Validate this developed predictive model against the fatigue data of SS316L, and (4) Assess the effects of defects/microstructure on the high strain rate behavior of AM IN718. To achieve these objectives, a rigorous research program integrating AM fabrication, fatigue and high strain rate experiments, analysis, and numerical simulations —both conventional linear elastic finite element method and crystal plasticity— will be carried out by a team of researchers at The National Center for Additive Manufacturing Excellence (NCAME) at Auburn University, University of Alabama-Tuscaloosa, and University of Alabama-Huntsville. The experimental effort serves to provide foundational data as well as initial knowledge on the defect-microstructure synergy. The design of experiments (DoE) is devised to achieve independent control of the AM alloys’ microstructural features and to evaluate the individual/synergistic effects of these features on the fatigue and high strain rate behaviors of AM alloys. The combined effect of defects/micro-structure on the high strain rate behavior of LB-PBF materials is currently not well understood, and the knowledge generated in this project serves to fill this gap. In addition to the experiments, a more complete picture regarding the defect/microstructure synergy on the fatigue behavior of these materials will be provided by parametric numerical simulations. The collective findings regarding the interrelationship between defect/microstructure and fatigue performance will then be cast into a predictive model. Such a model can enable the prediction of fatigue performance of LB-PBF components based on the most critical volumetric defect and the microstructure of the material. It can also be later extended to capture the stochastic effects of both volumetric and surface defects and/or other types of loading, such torsion and multiaxial. Key components of this research not only align well with several of NASA interest areas under the 2020 NASA Taxonomy, but they also address many technical gaps identified in both the AMSC and NIST roadmaps. In fact, this research has already attracted significant interest from several NASA research centers as witness by the NASA support letters. In addition, this research led by NCAME is also highly aligned with the Alabama EPSCoR State Science & Technology Roadmap and the “Strong Start, Strong Finish” initiative on advanced manufacturing, as noted by the support letter from Governor Ivey. Through this project, not only the team’s relevant technical capabilities will be enhanced, but also the collaboration within the multi-university team will be strengthened, preparing the team for future opportunities.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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