On the evolution of microstructure and defect control in 316L SS components fabricated via directed energy deposition

Journal Article · Mon Sep 09 00:00:00 EDT 2019 · Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing

DOI:https://doi.org/10.1016/j.msea.2019.138243· OSTI ID:1559510

Zheng, B. ^[1]; Haley, J. C. ^[1]; Yang, N. ^[2]; Yee, J. ^[2]; Terrassa, K. W. ^[1]; Zhou, Y. ^[1]; Lavernia, E. J. ^[1]; Schoenung, J. M. ^[1]

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1. Univ. of California, Irvine, CA (United States)
2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

To identify the critical issues that affect the evolution of microstructure during additive manufacturing, we investigated the influence of process parameters on the evolution of the dimensional and surface quality, microstructure, internal defects, and mechanical properties in 316L stainless steel (SS) components fabricated using laser engineered net shaping (LENS®), a directed energy deposition (DED) additive manufacturing (AM) technique. The results show that the accumulation of un-melted powder particles on the side walls of deposited sections can be avoided by selecting a laser under-focused condition. Moreover, we report that the variation of melt pool width is more sensitive to laser power than to the depth of the melt pool. The formation of a so-called “hierarchical” microstructure with cellular morphology is attributable to a combination of layer deposition and rapid solidification, which are characteristics of AM. Finally, we discuss microstructure evolution and defect formation, particularly the formation of multiple interfaces and the presence of un-melted powder particles and pores, in light of the dynamic convective fluid flow and rapid solidification that occur in the melt pool. X-ray computed tomography (X-CT) was used to precisely map the spatial distribution of pores in the DED components. The evolution of microstructure during DED is discussed in the context of related thermal phenomena in an effort to provide fundamental insight into the mechanisms that govern defect formation.

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1559510
• Alternate ID(s): OSTI ID: 1563048
• Report Number(s): SAND2019-9333J; 678327; TRN: US2000354
• Journal Information: Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing, Vol. 764, Issue C; ISSN 0921-5093
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE