Localized melt-scan strategy for site specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing

Raghavan, Narendran; Simunovic, Srdjan; Dehoff, Ryan R.; Plotkowski, Alex; Turner, John A.; Kirka, Michael M.; Babu, S. S.

doi:10.1016/j.actamat.2017.08.038

Cited by 168 publications

(54 citation statements)

References 30 publications

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“…Another interesting feature, in parts manufactured by additive manufacturing, is the capability to control texture along the part. For example, recent works have shown that by changing the scan strategy it is possible to modify the grain characteristics along the part [5,[97][98][99]. Texture control in fusion welding is significantly more difficult.…”

Section: Microstructural Effects In Fusion-based Additive Manufacturingmentioning

confidence: 99%

“…Increasing the functionally of the as-built parts often requires changing the grain morphology and orientation in site-specific locations, which primarily depend on the solidification conditions. The control of the grain morphology was demonstrated for both laser [83] and electron beam [99,159] powder-bed additive manufacturing. Though different in nature, these works rationalized the grain size and morphology evolution based on the combined effect of the thermal gradient and solidification rate, which, similar to fusion-based welding [61], dictate the grain size and morphology in the fusion zone.…”

Section: Modulation Of the Heat Sourcementioning

confidence: 99%

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Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Oliveira

Santos

Miranda

2020

Progress in Materials Science

422

134

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Additive manufacturing technologies based on melting and solidification have considerable similarities with fusion-based welding technologies, either by electric arc or high-power beams. However, several concepts are being introduced in additive manufacturing which have been extensively used in multipass arc welding with filler material. Therefore, clarification of fundamental definitions is important to establish a common background between welding and additive manufacturing research communities. This paper aims to review these concepts, highlighting the distinctive characteristics of fusion welding that can be embraced by additive manufacturing, namely the nature of rapid thermal cycles associated to small size and localized heat sources, the non-equilibrium nature of rapid solidification and its effects on: internal defects formation, phase transformations, residual stresses and distortions. Concerning process optimization, distinct criteria are proposed based on geometric, energetic and thermal considerations, allowing to determine an upper bound limit for the optimum hatch distance during additive manufacturing. Finally, a unified equation to compute the energy density is proposed. This equation enables to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size.

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Section: Microstructural Effects In Fusion-based Additive Manufacturingmentioning

confidence: 99%

Section: Modulation Of the Heat Sourcementioning

confidence: 99%

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Oliveira

Santos

Miranda

2020

Progress in Materials Science

422

134

View full text Add to dashboard Cite

show abstract

“…Therefore, weldable, precipitation strengthened alloys like IN718 have been among the first alloys adopted to AM with notable success across multiple AM processes; e.g. powder bed fusion by laser (L-PBF) [4], powder bed fusion by electron beam (EB-PBF) [49,50], directed energy deposition by laser [51], and directed energy deposition by plasma arc [46]. The fast cooling rates (10 3 -10 8 K/s) of AM processes leads to distinct microstructures in bulk AM parts compared with those produced through traditionally manufactured routes.…”

Section: Structure-property Relationshipsmentioning

confidence: 99%

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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“…The YXZ plane relates to the faces which were perpendicular to the build direction while the ZXY plane relates to the faces parallel to the build direction. The LB-PBF microstructure analysis revealed a strong < 011 > texture as a result of the < 001 > easy growth direction and the high solidification rate [25][26][27]. Additionally, the LB-PBF microstructure evolution results in a much finer average grain size (12 and 13 μm in the YXZ and ZXY planes, respectfully) than the wrought counterpart (54 μm equiaxed).…”

Section: Establishing Process-structure-property Relationshipsmentioning

confidence: 97%

Additive manufacturing of fatigue resistant austenitic stainless steels by understanding process-structure–property relationships

Pegues

Roach

Shamsaei

2019

Materials Research Letters

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The limited understanding of additive manufacturing process-structure-property interrelationships raises some concerns regarding the structural reliability, which limits the adoption of this emerging technology. In this study, laser beam-powder bed fusion is leveraged to fabricate an austenitic stainless steel with a microstructure containing minimal known crack initiation features. Ex-situ microstructural observations of the crack initiation features and mechanisms are carried out for interrupted fatigue tests via electron backscatter diffraction mapping of the micro-cracks. Results show that the additive manufactured stainless steel alloy has improved fatigue resistance compared to its wrought counterpart as a result of the unique microstructural features. IMPACT STATEMENT Using an experimental ex-situ microstructural investigation, the fatigue resistance of additive manufactured 304L stainless steel was shown to be superior to the wrought counterpart by avoiding the typical failure mechanisms.

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Localized melt-scan strategy for site specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing

Cited by 168 publications

References 30 publications

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

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

Additive manufacturing of fatigue resistant austenitic stainless steels by understanding process-structure–property relationships

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