Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718

Goel, Sneha; Sittiho, Anumat; Charit, Indrajit; Klement, Uta; Joshi, Shrikant V.

doi:10.1016/j.addma.2019.06.002

Cited by 27 publications

(19 citation statements)

References 59 publications

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“…In recent years, increasing attention has been focused on the hot isostatic pressing (HIP) of the Inconel 718 alloy which has a fine uniform microstructure and good mechanical properties [11][12][13][14]. Chang et al [15] indicated that HIP treatment of the Inconel 718 superalloy can make the grain uniform, 2 of 14 improve the segregated structure, and decrease the porosity by 85.8%.…”

Section: Introductionmentioning

confidence: 99%

Effects of the γ″-Ni3Nb Phase on Mechanical Properties of Inconel 718 Superalloys with Different Heat Treatments

Ling

Yin

et al. 2019

Materials

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The effects of the γ″-Ni3Nb phase on the mechanical properties of Inconel 718 superalloys, with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging, were characterized by morphological observation, X-ray diffraction, and tensile experiments. The results of the morphological observation revealed that many fine γ″ precipitates of ~26.49 ± 1.82 nm in mean size were formed in all samples. However, the relatively coarser γ″ precipitates formed in the grain boundaries were only observed in the sample treated with hot isostatic pressing + direct aging. The yield strengths of the hot isostatic pressing + direct aging sample at room temperature and at 650 °C both exhibited the maximum values about 993 ± 5.7 and 811 ± 12.6 MPa, respectively. The γ″ precipitate was considered to be the dominant strengthening phase in the sample according to the lattice misfits (ε) of γ/γ″. The strengthening mechanism of the samples can be explained as the coherency strain strengthening of fine γ″ precipitates. Moreover, due to the coarser γ″ precipitates in the grain boundaries, dislocation-cut ordered particle strengthening also occurred in the sample after hot isostatic pressing + direct aging treatment.

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Section: Introductionmentioning

confidence: 99%

Effects of the γ″-Ni3Nb Phase on Mechanical Properties of Inconel 718 Superalloys with Different Heat Treatments

Ling

Yin

et al. 2019

Materials

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“…However, it has been shown that the directional agglomerate of porosities is more likely to be responsible for the experimentally observed anisotropy, rather than the intrinsic crystallographic properties [96]. A similar indication can also be given by comparison made between the tensile properties of before and after HIP specimens [95], where after HIP the anisotropy is almost ignorable while the columnar feature is still maintained, and HIP is believed to reduce the porosities inherited from manufacturing process [95,98]. However, at elevated temperature when intergranular fracture becomes predominant, anisotropy might also be expected due to the relative orientation between the elongated columnar grain boundary and loading direction.…”

Section: Ebm In718mentioning

confidence: 78%

“…For the EBM cases, the very different grain growth behaviours are observed in contour and hatch region after HIP at 1200 • C/120 MPa/4 hours: noticeable grain growth is present in the contour region but not in the hatch region [127,128]. In addition, even for the columnar grains of EBM IN718, the coarsening behaviours can be different from one case to another, due to the presence of grain boundary carbide and its impinging effect [98,129,130]. Comparatively, as mentioned, the as-built SLM IN718 usually associates with large residual stress than the as-built EBM counterpart, which can provide an additional driving force for grain growth.…”

Section: Ebm and Slm In718mentioning

confidence: 98%

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On the Microstructures and Anisotropic Mechanical Behaviours of Additively Manufactured IN718

Deng

2019

Linköping Studies in Science and Technology. Dissertations

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Additive manufacturing (AM), also known as 3D printing, offers great design flexibility for manufacturing components with complex geometries, and has attracted significant interest in the aero and energy industries in the past decades. Among the commercial AM processes, selective laser melting (SLM) and electron beam melting (EBM) are the two most widely used ones for metallic materials. Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties, weldability and low cost. Due to its excellent weldability, IN718 has been intensively applied in the AM filed, to gain more understanding of the AM processes and fully realize AM's potentials. The study objects in the present thesis include both EBM and SLM IN718. The solidification conditions in EBM and SLM are very different and are different to that of conventional cast, leading to unique microstructures mechanical properties. Therefore, this thesis aims to gain better understanding of the microstructures and anisotropic mechanical behaviours of both EBM and SLM IN718, by detailed characterizations and by comparisons with the forged counterpart. The as-built microstructure of EBM IN718 is spatially dependent: the periphery (contour) region has a mixture of equiaxed and columnar grains, while the bulk (hatch) region has columnar grains elongated along the building direction; the last solidified region close to the top sample surface shows segregation and Laves phases, otherwise the rest of the whole sample is well homogenized. Differently, the as-built microstructure of SLM IN718 is spatially homogeneous: the grains is rather equiaxed and with subgrain cell structures. These microstructures also respond differently to the standard heat treatment routines for the conventional counterparts. Anisotropic mechanical properties are evident in the room temperature tensile tests and high temperature dwell-fatigue tests. The anisotropic tensile properties of EBM IN718 at room temperature are more likely due to the directional alignment of porosities along the building direction rather than the strong crys-In these papers I have been the main contributor, performing all the experimental work, characterization, analysis and manuscript writing, under the supervision of Johan Moverare and Ru Lin Peng.

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“…However, EBM-manufactured Alloy 718 is typically characterized by the presence of inevitable defects such as lack of fusion, gas porosity, and shrinkage porosity, which can be detrimental to the mechanical properties of the material [6]. Therefore, thermal post-treatment involving hot isostatic pressing (HIPing) is typically employed to reduce such defects in the AM manufactured material [3,[7][8][9]. In this context, it is pertinent to state that micro-computed tomography is used to obtain detailed information about the location and size of defects present in the material in 3D [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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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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Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718

Cited by 27 publications

References 59 publications

Effects of the γ″-Ni3Nb Phase on Mechanical Properties of Inconel 718 Superalloys with Different Heat Treatments

Effects of the γ″-Ni3Nb Phase on Mechanical Properties of Inconel 718 Superalloys with Different Heat Treatments

On the Microstructures and Anisotropic Mechanical Behaviours of Additively Manufactured IN718

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

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