Dynamic solidification behavior during metal additive manufacturing directly influences the as-built microstructure, defects, and mechanical properties of printed parts. How the formation of these features is driven by temperature variation (e.g., thermal gradient magnitude and solidification front velocity) has been studied extensively in metal additive manufacturing, with synchrotron x-ray imaging becoming a critical tool to monitor these processes. Here, we extend these efforts to monitoring full thermomechanical deformation during solidification through the use of operando x-ray diffraction during laser melting. With operando diffraction, we analyze thermomechanical deformation modes such as torsion, bending, fragmentation, assimilation, oscillation, and interdendritic growth. Understanding such phenomena can aid the optimization of printing strategies to obtain specific microstructural features, including localized misorientations, dislocation substructure, and grain boundary character. The interpretation of operando diffraction results is supported by post-mortem electron backscatter diffraction analyses.
This content will become publicly available on December 1, 2024
Functionally graded stainless steels with tailored grain boundary serration
We demonstrate the possibility of spatially controlling the degree of grain boundary serration in functionally graded stainless steels, by alloying powder mixtures on-the-fly during directed energy deposition additive manufacturing. Grain boundary serration is an attractive feature in polycrystalline microstructures, as it confers superior resistance to crack propagation and hot corrosion. Quantitative measurements at the microstructure scale coupled with thermodynamic calculations allow us to propose a mechanism to explain the origin of grain boundary serration. The formation of transient δ ferrite during solidification and its subsequent dissolution during cooling, governed by the Cr/Ni ratio, leads to the formation of remnant ferrite particles that hinder the growth of austenite grains in the solid state via a Smith-Zener pinning phenomenon. This finding opens new perspectives for grain boundary engineering, in-situ during additive manufacturing.
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- NSF-PAR ID:
- 10481567
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Scripta Materialia
- Volume:
- 237
- Issue:
- C
- ISSN:
- 1359-6462
- Page Range / eLocation ID:
- 115714
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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