Toward a Better Understanding of Phase Transformations in Additive Manufacturing of Alloy 718

Kumara, Chamara; Balachandramurthi, Arun Ramanathan; Goel, Sneha; Hanning, Fabian; Moverare, Johan

doi:10.2139/ssrn.3628004

Cited by 4 publications

(7 citation statements)

References 43 publications

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“…The high hardness and significant precipitation of c 00 phase as shown in Fig. 10 achieved through ST with FC reveals interesting prospects in tailoring cooling rate after ST as an alternative to carrying out a separate subsequent aging treatment as also recently reported by Kumara et al [40]. For instance, in oil-field applications, Special Metals Corp. has suggested a maximum hardness of Alloy 718 to be 40 HRC (382 kgf/mm 2 [58]) [59] which is significantly below the peak hardness of the material (* 500 kgf/mm 2 ) [18].…”

Section: Potential To Design Shorter Tailored Posttreatment For Ebm Asupporting

confidence: 59%

“…An earlier study on wrought Alloy 718 quantified d phase and showed higher amount of d phase formation after ST at 950°C compared to 975°C; both treatments performed for a constant duration of 2 h [39]. Simulation results have also shown higher equilibrium volume fraction of d phase at 954°C than at 980°C [40]. Therefore, depending on the required microstructural properties appropriate ST conditions should be employed, as increase in d phase content has been reportedly associated with reduced amount of strengthening phase c 00 [49], because precipitation of both d and c 00 phases compete for available Nb in the material [50].…”

Section: Solution Treatmentmentioning

confidence: 88%

“…5). Simulation results have shown a decrease in the equilibrium volume fraction of d phase due to reduced elemental segregation [40]. Mitchell et al [41] have also experimentally observed precipitation of d phase to be highly dependent on the local Nb concentration.…”

Section: Solution Treatmentmentioning

confidence: 98%

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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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Section: Potential To Design Shorter Tailored Posttreatment For Ebm Asupporting

confidence: 59%

Section: Solution Treatmentmentioning

confidence: 88%

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

et al. 2020

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“…In non-equilibrium solidification, the γ matrix begins to solidify when the temperature is below the liquidus temperature during the first several thermal cycles. The segregation of Inconel 718 component elements changes the driving force of phase formation, which leads to the formation of Laves phases in the interdendritic region [60]. It has been reported that Laves formation is related to slow solidification at a low cooling rate [61].…”

Section: Discussionmentioning

confidence: 99%

Data driven analysis of thermal simulations, microstructure and mechanical properties of Inconel 718 thin walls deposited by metal additive manufacturing

Fang¹,

Cheng²,

Glerum³

et al. 2021

Preprint

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The extreme and repeated temperature variation during additive manufacturing of metal parts has a large effect on the resulting material microstructure and properties. The ability to accurately predict this temperature field in detail, and relate it quantitatively to structure and properties, is a key step in predicting part performance and optimizing process design. In this work, a finite element simulation of the Directed Energy Deposition (DED) process is used to predict the space-and time-dependent temperature field during the multi-layer build process for Inconel 718 walls. The thermal model is validated using the dynamic infrared (IR) images captured in situ during the DED builds, showing good agreement with experimental measurements. The relationship between predicted cooling rate, microstructural features, and mechanical properties is examined, and cooling rate alone is found to be insufficient in giving quantitative property predictions. Because machine learning offers an efficient way to identify important features from series data, we apply a 1D convolutional neural network (CNN) data-driven framework to automatically extract the dominant predictive features from simulated temperature history. The relationship between the CNN-extracted features and the mechanical properties is studied. To interpret how CNN performs in intermediate layers, we visualize the extracted features produced on each convolutional layer by a trained CNN. Our results show that the results predicted by the CNN agree well with experimental measurements and give insights for physical mechanisms of microstructure evolution and mechanical properties.

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“…The austenite phase is strengthened by precipitating γ' (Ni (Al, Ti)) and γ'' (Ni 3 Nb) phases. However, it also forms some harmful intermetallic phases at the time of processing such as δ (Ni 3 Nb) with orthorhombic DO a structure and laves (Ni, Fe, Cr) 2 (Nb, Mo, Ti) phases with a hexagonal crystal structure due to more segregation of Nb and Mo elements [4][5][6][7]. The desired properties of the alloy can be restored by eliminating the intermetallic phases and increasing the presence of strengthening phases [8].…”

Section: Introductionmentioning

confidence: 99%

Attainment of Favorable Microstructure for Residual Stress Reduction Through High-Temperature Heat Treatment on Additive Manufactured Inconel 718 Alloy

Jebaraj

2022

Preprint

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The mitigation of residual stress in additive manufactured metal parts through post-heat treatment helps to enhance life during service. The present work aims to investigate the effect of the high-temperature heat treatment at 1065°C on microstructural changes, residual stress patterns, and hardness of Inconel 718 metal blocks fabricated through the Laser powder bed fusion (L-PBF) process. The non-destructive X-ray diffraction technique known as cos α method was used to measure the surface residual stress by capturing the Debye ring. It was found that the existence of columnar dendrites with laves phases in the interdendritic region along the building direction was dissolved after heat treatment. The resultant microstructure showed homogeneous equiaxed grains with the formation of annealing twins along with strengthening phases (γ’ and γ’’) and tiny metal carbides on the grain boundaries. Further, the residual stress magnitude in the as-built sample was found to be 77% higher on the corners compared to the center region of the top surface. The average value of residual stress on the top surface was found to be 35.5% lesser than the lateral side surface of the sample. It was observed that the distribution of residual stress is not uniform in as-built condition. The heat-treated sample showed uniform distribution of compressive residual stresses in all the locations. This phenomenon happened due to the increase in diffusion of atoms present in the high-stress regions migrated to low-stress regions till attain their equilibrium condition. During this action, the stresses present in the grain interiors were altered considerably and resulted in complete recrystallization with the precipitation of more strengthening phases and annealing twins. The high-temperature post-heat treatment also affects the hardness leads to 23.03% increase in average microhardness mainly induced resistance to dislocation motion by precipitation of strengthening phases in the γ matrix.

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Toward a Better Understanding of Phase Transformations in Additive Manufacturing of Alloy 718

Cited by 4 publications

References 43 publications

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

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

Data driven analysis of thermal simulations, microstructure and mechanical properties of Inconel 718 thin walls deposited by metal additive manufacturing

Attainment of Favorable Microstructure for Residual Stress Reduction Through High-Temperature Heat Treatment on Additive Manufactured Inconel 718 Alloy

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