Title: Origin of dislocation structures in an additively manufactured austenitic stainless steel 316L

Abstract

In this experiment, the origin of dislocation structures in AM stainless steels was systematically investigated by controlling the effect of thermal stress through geometric constraints for the first time. Stainless steel 316L parts were produced in the form of “1D” rods, “2D” walls, and "3D" rectangular prisms to evaluate the effect of constraints to thermal expansion/shrinkage on the development of defect microstructures and to elucidate the origin of additively manufactured (AM) dislocation microstructures. Dislocation density, organization, chemical micro-segregation, precipitate structures, and misorientations were analyzed as a function of increasing constraints around solidifying material in 1D, 2D, and 3D components built using both directed energy deposition (DED) and powder-bed selective laser melting (SLM). In DED parts, the dislocation density was not dependent on local misorientations or micro-segregation patterns, but evolved from approximately ρ_⊥ = 10¹² m^-2 in 1D parts to ρ_⊥ = 10¹⁴ m^-2 in 3D parts, indicating that it is primarily thermal distortions that produce AM dislocation structures. In DED 3D parts and SLM parts, dislocation densities were highest (ρ_⊥ ≈ 10¹⁴ m^-2) and corresponded to the formation of dislocation cells approximately 300-450 nm in diameter. Dislocation cells overlapped with dendrite micro-segregation in some but not all cases. The resultsmore » illustrate that dendritic micro-segregation, precipitates, or local misorientations influence how the dislocations organize during processing, but are not responsible for producing the organized cell structures. Furthermore, this work shows that AM dislocation structures originate due to thermal distortions during printing, which are primarily dictated by constraints surrounding the melt pool and thermal cycling.« less

Authors:

Bertsch, K. M. ^[1]; Meric de Bellefon, G. ^[2]; Kuehl, B. ^[2]; Thoma, D. J. ^[2]

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+ Show Author Affiliations

1. Univ. of Wisconsin, Madison, WI (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Univ. of Wisconsin, Madison, WI (United States)

Publication Date:

Fri Aug 14 00:00:00 EDT 2020

Research Org.:

Georgia Institute of Technology, Atlanta, GA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); NSF-DMREF

OSTI Identifier:

1690234

Alternate Identifier(s):

OSTI ID: 1648371

Grant/Contract Number:  

NA0003921; DMR-1728933; CMMI-1561899; AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Acta Materialia

Additional Journal Information:

Journal Volume: 199; Journal ID: ISSN 1359-6454

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Additive manufacturing; Dislocations; Dendrites; Transmission electron microscopy; Orientation mapping