Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Goel, Sneha; Ahlfors, Magnus; Bahbou, Fouzi; Joshi, Shrikant V.

doi:10.1007/s11665-018-3712-0

Cited by 38 publications

(24 citation statements)

References 18 publications

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“…This value is close to the reported peak hardness (~490 kgf/mm 2 ) of Alloy 718 [10]. Previous studies on EBM Alloy 718 have also reported an increase in hardness in the as-built condition from 410 kgf/mm 2 to 470 kgf/mm 2 after aging [32][33][34]. Thus, the foregoing results amply reveal that, regardless of the vastly different defect content in the as-built condition, the final post-treated condition exhibits a very similar density (Figure 3), phase constitution in terms of δ phase and γ" phase distribution ( Figures 5 and 6), as well as microhardness values (Figure 7).…”

Section: Resultssupporting

confidence: 88%

Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?

et al. 2020

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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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Section: Resultssupporting

confidence: 88%

Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?

et al. 2020

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“…These results corroborate the observations of Balachandramurthi et al [9], who have also reported the grain growth after HIPing of EBM Alloy 718 at 1200°C to be mainly restricted to the contour region. In other studies employing HIPing at 1200°C, too, extensive grain growth in the hatch region was observed [12,26].…”

Section: Grain Structurementioning

confidence: 83%

“…Prior to HIPing, all the specimens were subjected to ultrasonic cleaning. Here it should be mentioned that prior work by authors has already established uniformity in the EBM build [26]. The selection of conditions for HIP1 (1120°C, 100 MPa, 4 h) and HIP2 (1185°C, 100 MPa, 4 h) was based on the suggestions in the ASTM F3055 standard for powder bed fusion built Alloy 718 [19].…”

Section: Thermal Post-treatmentsmentioning

confidence: 99%

Microstructure evolution-based design of thermal post-treatments for EBM-built Alloy 718

et al. 2020

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Alloy 718 samples were fabricated by electron beam melting (EBM) additive manufacturing process. The work focused on systematic investigation of response of the material to various thermal post-treatments, involving hot isostatic pressing (HIPing), solution treatment (ST) and two-step aging, to tailor post-treatment procedure for EBM-built Alloy 718. Results showed that HIPing at lowered temperature can be used for attaining desired defect closure while preserving grain size. Subjecting the material to ST, with or without prior HIPing, mainly caused precipitation of δ phase at the grain boundaries with prior HIPing decreasing the extent of δ phase precipitation. Moreover, results suggest that the utility of ST, with prior HIPing, could be dictated by the need to achieve a certain δ phase content, as the typically targeted homogenization after ST had already been achieved through HIPing. Detailed investigation of microstructural evolution during subsequent aging with and without prior HIPing showed that a significantly shortened aging treatment (‘4 + 1’ h), compared to the ‘standard’ long treatment (‘8 + 8’ h) traditionally developed for conventionally produced Alloy 718, might be realizable. These results can have significant techno-economic implications in designing tailored post-treatments for EBM-built Alloy 718. Graphical abstract

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“…This has been an important motivation behind this study. Although prior work by the authors has involved investigation of aspects related to uniformity in a typical EBM Alloy 718 build, [23] inclusions and precipitates in as-built and post-treated material, [24] extent of defect closure during HIPing in builds with intentionally introduced defects, [25] etc., the response of hatch and contour regions to identical post-treatments remains not fully investigated.…”

Section: Introductionmentioning

confidence: 99%

As-Built and Post-treated Microstructures of an Electron Beam Melting (EBM) Produced Nickel-Based Superalloy

Goel

Mehtani

Yao

et al. 2020

Metall Mater Trans A

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The microstructures of an electron beam melted (EBM) nickel-based superalloy (Alloy 718) were comprehensively investigated in as-built and post-treated conditions, with particular focus individually on the contour (outer periphery) and hatch (core) regions of the build. The hatch region exhibited columnar grains with strong 〈001〉 texture in the build direction, while the contour region had a mix of columnar and equiaxed grains, with no preferred crystallographic texture. Both regions exhibited nearly identical hardness and carbide content. However, the contour region showed a higher number density of fine carbides compared to the hatch. The as-built material was subjected to two distinct post-treatments: (1) hot isostatic pressing (HIP) and (2) HIP plus heat treatment (HIP + HT), with the latter carried out as a single cycle inside the HIP vessel. Both post-treatments resulted in nearly an order of magnitude decrease in defect content in hatch and contour regions. HIP + HT led to grain coarsening in the contour, but did not alter the microstructure in the hatch region. Different factors that may be responsible for grain growth, such as grain size, grain orientation, grain boundary curvature and secondary phase particles, are discussed. The differences in carbide sizes in the hatch and contour regions appeared to decrease after post-treatment. After HIP + HT, similar higher hardness was observed in both the hatch and contour regions compared to the as-built material.

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Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Cited by 38 publications

References 18 publications

Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?

Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?

Microstructure evolution-based design of thermal post-treatments for EBM-built Alloy 718

As-Built and Post-treated Microstructures of an Electron Beam Melting (EBM) Produced Nickel-Based Superalloy

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