Microstructural control of alloy 718 fabricated by electron beam melting with expanded processing window by adaptive offset method

Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to <0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.

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Encapsulation of Electron Beam Melting Produced Alloy 718 to Reduce Surface Connected Defects by Hot Isostatic Pressing

Materials ◽

10.3390/ma13051226 ◽

2020 ◽

Vol 13 (5) ◽

pp. 1226 ◽

Cited By ~ 1

Author(s):

Yunus Emre Zafer ◽

Sneha Goel ◽

Ashish Ganvir ◽

Anton Jansson ◽

Shrikant Joshi

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Surface Defects ◽

High Surface ◽

Hot Isostatic Pressing ◽

Coated Sample ◽

Alloy 718 ◽

Isostatic Pressing ◽

Before And After ◽

X Ray Computed

Defects in electron beam melting (EBM) manufactured Alloy 718 are inevitable to some extent, and are of concern as they can degrade mechanical properties of the material. Therefore, EBM-manufactured Alloy 718 is typically subjected to post-treatment to improve the properties of the as-built material. Although hot isostatic pressing (HIPing) is usually employed to close the defects, it is widely known that HIPing cannot close open-to-surface defects. Therefore, in this work, a hypothesis is formulated that if the surface of the EBM-manufactured specimen is suitably coated to encapsulate the EBM-manufactured specimen, then HIPing can be effective in healing such surface-connected defects. The EBM-manufactured Alloy 718 specimens were coated by high-velocity air fuel (HVAF) spraying using Alloy 718 powder prior to HIPing to evaluate the above approach. X-ray computed tomography (XCT) analysis of the defects in the same coated sample before and after HIPing showed that some of the defects connected to the EBM specimen surface were effectively encapsulated by the coating, as they were closed after HIPing. However, some of these surface-connected defects were retained. The reason for such remnant defects is attributed to the presence of interconnected pathways between the ambient and the original as-built surface of the EBM specimen, as the specimens were not coated on all sides. These pathways were also exaggerated by the high surface roughness of the EBM material and could have provided an additional path for argon infiltration, apart from the uncoated sides, thereby hindering complete densification of the specimen during HIPing.

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Processing window and evaporation phenomena for Ti–6Al–4V produced by selective electron beam melting

Acta Materialia ◽

10.1016/j.actamat.2014.05.037 ◽

2014 ◽

Vol 76 ◽

pp. 252-258 ◽

Cited By ~ 94

Author(s):

V. Juechter ◽

T. Scharowsky ◽

R.F. Singer ◽

C. Körner

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Processing Window ◽

Selective Electron Beam Melting

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

Materials ◽

10.3390/ma14205953 ◽

2021 ◽

Vol 14 (20) ◽

pp. 5953

Author(s):

Ahmad Raza ◽

Eduard Hryha

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Elevated Temperatures ◽

Ion Beam ◽

High Vacuum ◽

Alloying Elements ◽

Heat Shield ◽

Alloy 718 ◽

Feedstock Powder ◽

Heat Shields

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.

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