Effect of Powder Recycling on Defect Formation in Electron Beam Melted Alloy 718

Gruber, Hans; Luchian, Cosmina; Hryha, Eduard; Nyborg, Lars

doi:10.1007/s11661-020-05674-8

Cited by 26 publications

(11 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As observed in earlier studies, [3,26,29] during the actual melting process, there is a risk of transferring of nonmetallic phases (mainly Al-rich oxide and TiN) from the powder to the components. Furthermore, since these phases tend to accumulate into larger sized clusters or oxide flakes, they act as potential damage initiation sites, especially under cyclic loading conditions.…”

Section: Discussionmentioning

confidence: 61%

Effect of Powder Recycling in Electron Beam Melting on the Surface Chemistry of Alloy 718 Powder

Gruber

Henriksson

Hryha

et al. 2019

Metall Mater Trans A

Self Cite

View full text Add to dashboard Cite

Process-induced degradation of the powder feedstock in additive manufacturing may have a negative influence on the final properties of built components. Consequently, it may lower the cost-effectiveness of powder bed additive manufacturing, which relies on recycling of the nonconsumed powder. This is especially the case for production of high-performance aero engine components where high material and process reliability is required. This study comprises a detailed investigation on the degradation of Alloy 718 powder during multicycle electron beam melting (EBM). The surface-sensitive analysis methods, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), were combined with scanning electron microscopy (SEM) to depict the differences in surface morphology, and surface composition of powder samples exposed to varying numbers of re-use cycles. The results show a significant change in surface characteristics after exposing the powder to the process and the environment in the build chamber. The virgin powder is covered mainly by a relatively thin and homogeneous oxide layer. The re-used powder, however, has undergone transformation to a heterogeneous oxide layer, rich in thermodynamically stable Al-rich oxide particulates, which started already during the first build cycle. Significant growth of the Al-rich oxide occurs via selective oxidation of Al under the conditions in the build chamber, including both pickup of oxygen from the process atmosphere and redistribution of initial surface-bound oxygen from less-stable products like Ni-oxide and/or hydroxide.

show abstract

Section: Discussionmentioning

confidence: 61%

Effect of Powder Recycling in Electron Beam Melting on the Surface Chemistry of Alloy 718 Powder

Gruber

Henriksson

Hryha

et al. 2019

Metall Mater Trans A

Self Cite

View full text Add to dashboard Cite

show abstract

“…Such accumulation of inclusions has already been reported for Alloy 718 produced by other AM processes. Gruber et al [28] revealed the transport and accumulation of oxide and nitride inclusions, which cluster in the liquid metal, at the top and side surfaces of components built by EBM. As a result, a refining effect was proposed explaining almost a 50% reduction in oxygen content in the EBM-produced compact compared to the feedstock powder, which is valid even in case of powder re-use after 30 cycles [28].…”

Section: Discussionmentioning

confidence: 99%

“…Gruber et al [28] revealed the transport and accumulation of oxide and nitride inclusions, which cluster in the liquid metal, at the top and side surfaces of components built by EBM. As a result, a refining effect was proposed explaining almost a 50% reduction in oxygen content in the EBM-produced compact compared to the feedstock powder, which is valid even in case of powder re-use after 30 cycles [28]. It should be emphasized that TiN and Al 2 O 3 are expected to float in the liquid metal because of their low densities in comparison to the metal matrix (i.e., TiN: 5.4 g/cm 3 , Al 2 O 3 : 4.0 g/cm 3 , Alloy 718: 8.2 g/cm 3 ) [26].…”

Section: Discussionmentioning

confidence: 99%

“…However, as suggested by Polonsky et al [29], the rapid cooling and solidification rates during AM processing will tend to limit the effect of buoyancy, and instead, the Marangoni flow is more likely to be responsible for the displacement and clustering of the inclusions. As shown by Gruber et al [28], strong oxide accumulation on the top of the specimen and specimen contour regions makes chemical analysis of the EBM-fabricated compacts very sensitive to the sampling of the specimens for chemical analysis. Since the chemistry reported in Table 1 was measured in samples extracted from the bulk without surfaces, additional analyses were conducted to measure the oxygen content close to the surfaces, by cutting and analyzing separately the side and top surfaces of the Argon 500 ppm O 2 cube.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion

Pauzon

Markström²,

Goff

et al. 2021

Metals

Self Cite

View full text Add to dashboard Cite

The detrimental effect of nitrogen and oxygen when it comes to the precipitation of the strengthening γ’’ and γ’ phases in Alloy 718 is well-known from traditional manufacturing. Hence, the influence of the two processing atmospheres, namely argon and nitrogen, during the laser powder bed fusion (L-PBF) of Alloy 718 parts was studied. Regardless of the gas type, considerable losses of both oxygen of about 150 ppm O2 (≈30%) and nitrogen on the level of around 400 ppm N2 (≈25%) were measured in comparison to the feedstock powder. The utilization of nitrogen as processing atmosphere led to a slightly higher nitrogen content in the as-built material—about 50 ppm—compared to the argon atmosphere. The presence of the stable nitrides and Al-rich oxides observed in the as-built material was related to the transfer of these inclusions from the nitrogen atomized powder feedstock to the components. This was confirmed by dedicated analysis of the powder feedstock and supported by thermodynamic and kinetic calculations. Rapid cooling rates were held responsible for the limited nitrogen pick-up. Oxide dissociation during laser–powder interaction, metal vaporization followed by oxidation and spatter generation, and their removal by processing atmosphere are the factors describing an important oxygen loss during L-PBF. In addition, the reduction of the oxygen level in the process atmosphere from 500 to 50 ppm resulted in the reduction in the oxygen level in as-built component by about 5%.

show abstract

“…For better energy efficiency and to circumvent the smoking effect, a high vacuum in the chamber to minimize electron beam attenuation and preheating of the powder bed to semi-sintering temperature to enhance the electronic conductivity of the powder bed are prerequisites of EBM [2,3]. Although preheating at elevated temperatures and high vacuum can improve the process stability, these processing conditions can affect the unused feedstock powder in the build chamber [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Spatter and Sublimation in Alloy 718 during Electron Beam Melting

Raza¹,

Hryha²

2021

Materials

Self Cite

View full text Add to dashboard Cite

Due to elevated temperatures and high vacuum levels in electron beam melting (EBM), spatter formation and accumulation in the feedstock powder, and sublimation of alloying elements from the base feedstock powder can affect the feedstock powder’s reusability and change the alloy composition of fabricated parts. This study focused on the experimental and thermodynamic analysis of spatter particles generated in EBM, and analyzed sublimating alloying elements from Alloy 718 during EBM. Heat shields obtained after processing Alloy 718 in an Arcam A2X plus machine were analyzed to evaluate the spatters and metal condensate. Comprehensive morphological, microstructural, and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB), and energy dispersive spectroscopy (EDS). The morphological analysis showed that the area coverage of heat shields by spatter increased from top (<1%) to bottom (>25%), indicating that the spatter particles had projectile trajectories. Similarly, the metal condensate had a higher thickness of ~50 μm toward the bottom of the heat shield, indicating more significant condensation of metal vapors at the bottom. Microstructural analysis of spatters highlighted that the surfaces of spatter particles sampled from the heat shields were also covered with condensate, and the thickness of the deposited condensate depended on the time of landing of spatter particles on the heat shield during the build. The chemical analysis showed that the spatter particles had 17-fold higher oxygen content than virgin powder used in the build. Analysis of the metalized layer indicated that it was formed by oxidized metal condensate and was significantly enriched with Cr due to its higher vapor pressure under EBM conditions.

show abstract

Effect of Powder Recycling on Defect Formation in Electron Beam Melted Alloy 718

Cited by 26 publications

References 25 publications

Effect of Powder Recycling in Electron Beam Melting on the Surface Chemistry of Alloy 718 Powder

Effect of Powder Recycling in Electron Beam Melting on the Surface Chemistry of Alloy 718 Powder

Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion

Characterization of Spatter and Sublimation in Alloy 718 during Electron Beam Melting

Contact Info

Product

Resources

About