Intrinsic strain aging, Σ3 boundaries, and origins of cellular substructure in additively manufactured 316L

Birnbaum, Andrew J.; Steuben, John C.; Barrick, Erin J.; Iliopoulos, Athanasios; Michopoulos, John G.

doi:10.1016/j.addma.2019.100784

Cited by 63 publications

(53 citation statements)

References 36 publications

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“…Moreover, the exact mechanism of dislocations generation during AM is still subject of discussion in literature [80,81]; however, our results in this work are consistent with the hypothesis that the formation of low-energy dislocation cell structures, even after rapid solidification,…”

Section: Solute Segregation and Misorientation Periodicities Dictate supporting

confidence: 90%

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Gallmeyer

Moorthy

Kappes

et al. 2020

Additive Manufacturing

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Dislocation structures, chemical segregation, γ′, γ″, ! precipitates and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure is revealed. Knowledge derived from these process-structure-property relationships was used to engineer a super-solvus solution anneal at 1020 ºC for 15 minutes, followed by aging at 720 ºC for 24 hours heat treatment for AM-IN718 that eliminates Laves and δ phases, preserves AM-specific dislocation cells that are shown to be stabilized by MC carbide particles, and precipitates dense γ′ and γ″ nanoparticle populations. This "optimized for AM-IN718 heat treatment" results in superior properties relative to wrought/additively manufactured, then industry standard heat treated IN718: relative increases of 7/10% in yield strength, 2/7% in ultimate strength, and 23/57% in elongation to failure are realized, respectively, regardless of as-built vs. machined surface finishes.

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Section: Solute Segregation and Misorientation Periodicities Dictate supporting

confidence: 90%

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Gallmeyer

Moorthy

Kappes

et al. 2020

Additive Manufacturing

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“…4b for the as-printed condition, likely derived from the original powder particle microstructure 87 . The bulk AM material,~50 μm below the surface, shows a typical PBF 316L microstructure with large (>20 μm) elongated, columnar grains and at higher magnifications (not shown), the dislocation cell substructure with solute (Cr/Mo) segregation, similar to what others have observed 88 . The pole figure map for the electro-polished sample, in Fig.…”

Section: Resultssupporting

confidence: 84%

How build angle and post-processing impact roughness and corrosion of additively manufactured 316L stainless steel

et al. 2020

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Additively manufactured austenitic stainless steels exhibit numerous microstructural and morphological differences compared to their wrought counterparts that will influence the metals corrosion resistance. The characteristic as-printed surface roughness of powder bed fusion (PBF) stainless steel parts is one of these morphological differences that increases the parts susceptibility to localized corrosion. This study experimentally determines the average surface roughness and breakdown potential (E b) for PBF 316L in 6 surface finished states: as-printed, ground with SiC paper, tumble polished in abrasive media, electro-polished, chemically passivated, and the application of a contour/re-melt scan strategy. In general, a smaller average surface roughness led to a larger E b. The smoothest surface treatments, ground and electro-polished conditions, led to E b near the materials limit (~+1.0 V Ag/AgCl) while all other surface treatments exhibited significantly lower E b (~+0.3 V Ag/AgCl) The build angle was also shown to impact surface roughness, where surfaces at high angles from the build direction resulted in larger roughness values, hence lower E b .

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“…Before continuing with the rationalization of the differences in RS state observed in the three investigated specimens, a brief description on the prior knowledge in the formation of dislocation cell structure is due. Even though the mechanisms controlling dislocation generation during AM are still subjected to debate in the literature [64,65], it is generally assumed that, independently of how they form, the periodic fluctuations in dislocation density are more stable than uniform arrays [66]. The spatial arrangement of the dislocation cell structure is controlled by the dendrite-cell geometries at the time of solidification [48].…”

Section: Considerations On the Rs Resultsmentioning

confidence: 99%

On the interplay of microstructure and residual stress in LPBF IN718

et al. 2020

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The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.

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Intrinsic strain aging, Σ3 boundaries, and origins of cellular substructure in additively manufactured 316L

Cited by 63 publications

References 36 publications

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

How build angle and post-processing impact roughness and corrosion of additively manufactured 316L stainless steel

On the interplay of microstructure and residual stress in LPBF IN718

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