Evolution of δ Phase Microstructure in Alloy 718

Sundararaman, M.; Nalawade, Sachin; Singh, J.B.; Verma, Amit Kumar; Paul, Bhaskar; Ramaswamy, Kishore

doi:10.1002/9781118495223.ch57

Cited by 23 publications

(16 citation statements)

References 16 publications

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“…The USAXS dimensionalities of the δ phase precipitates are also in good agreement with the values identified from the SEM results (after 8 h, diameter at (815 ± 157) nm and thickness at (48 ± 6) nm). Previous TEM micrographs of δ phase in AM IN625 heat-treated at 870 °C for 1 h demonstrated that the precipitates are highly crystalline and that the orientation relationship between the FCC matrix and δ phase precipitates follows {111} FCC //(100) δ and <11̄0> FCC //[100] δ , a result also identified in an earlier TEM study of δ phase in 718 alloy [23,82]. In particular, it was reported that in each close-packed plane, three variants of δ phase can form with their long axes aligned with the close-packed directions in the FCC matrix.…”

Section: Resultssupporting

confidence: 62%

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion

et al. 2018

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Elemental segregation is a ubiquitous phenomenon in additive-manufactured (AM) parts due to solute rejection and redistribution during the solidification process. Using electron microscopy, in situ synchrotron X-ray scattering and diffraction, and thermodynamic modeling, we reveal that in an AM nickel-based superalloy, Inconel 625, stress-relief heat treatment leads to the growth of unwanted δ-phase precipitates on a time scale much faster than that in wrought alloys (minutes versus tens to hundreds of hours). The root cause for this behavior is the elemental segregation that results in local compositions of AM alloys outside the bounds of the allowable range set for wrought alloys. In situ small angle scattering experiments reveal that platelet-shaped δ phase precipitates grow continuously and preferentially along their lateral dimensions during stress-relief heat treatment, while the thickness dimension reaches a plateau very quickly. In situ XRD experiments reveal that nucleation and growth of δ-phase precipitates occur within 5 min during stress-relief heat treatment, indicating a low nucleation barrier and a short incubation time. An activation energy for the growth of δ phase was found to be (131.04 ± 0.69) kJ mol−1. We further demonstrate that a subsequent homogenization heat treatment can effectively homogenize the AM alloy and remove the deleterious δ phase. The combined experimental and modeling methodology in this work can be extended to elucidate the phase evolution during heat treatments in a broad range of AM materials.

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Section: Resultssupporting

confidence: 62%

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion

et al. 2018

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“…In addition, the intergranular δ-phase was brighter than the intragranular ones due to its larger content of Nb. Presumably, the δ-phase started its precipitation at the grain boundaries; however, as the temperature or dwell time increased (lower cooling rate~300 K/s), the intragranular δ-phase precipitates can appear [29], as shown in Fig. 5b.…”

Section: Microstructures Of the Ebm Samples In All Groupsmentioning

confidence: 99%

Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 718

Karimi

Sadeghimeresht

Deng

et al. 2018

Int J Adv Manuf Technol

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Effects of build layout and orientation consisting of (a) height from the build plate (Z-axis), (b) distance between samples, and (c) location in the build plate (X-Y plane) on porosity, NbC fraction, and hardness in electron beam melted (EBM) Alloy 718 were studied. The as-built samples predominantly showed columnar structure with strong ˂001˃ crystallographic orientation parallel to the build direction, as well as NbC and δ-phase in inter-dendrites and grain boundaries. These microstructural characteristics were correlated with the thermal history, specifically cooling rate, resulted from the build layout and orientation parameters. The hardness and NbC fraction of the samples increased around 6% and 116%, respectively, as the height increased from 2 to 45 mm. Moreover, by increasing the height, formation of δ-phase was also enhanced associated with lower cooling rate in the samples built with a greater distance from the build plate. However, the porosity fraction was unaffected. Increasing the sample gap from 2 to 10 mm did not change the NbC fraction and hardness; however, the porosity fraction increased by 94%. The sample location in the build chamber influenced the porosity fraction, particularly in interior and exterior areas of the build plate. The hardness and NbC fraction were not dependent on the sample location in the build chamber.

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“…It is shown in Figure 12 (A_COS, B_COS and C_COS) that a few needle-like phases are precipitated in the interdendritic regions, including the Laves phase. The needle-like phases are identified as a δ-phase [21] and it is also observed by the XRD analysis. The presence of this δ-phase is more in the A_COS samples than in B_COS and C_COS samples.…”

Section: Apparition Of Laves Phase and Hot Cracking Formationmentioning

confidence: 78%

Influence of Heat Input on the Formation of Laves Phases and Hot Cracking in Plasma Arc Welding (PAW) Additive Manufacturing of Inconel 718

Artaza

Bhujangrao

Suárez

et al. 2020

Metals

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Nickel-based alloys have had extensive immersion in the manufacturing world in recent decades, especially in high added value sectors such as the aeronautical sector. Inconel 718 is the most widespread in terms of implantation. Therefore, the interest in adapting the manufacture of this material to additive manufacturing technologies is a significant objective within the scientific community. Among these technologies for the manufacture of parts by material deposition, plasma arc welding (PAW) has advantages derived from its simplicity for automation and integration on the work floor with high deposition ratios. These characteristics make it very economically appetizing. However, given the tendency of this material to form precipitates in its microstructure, its manufacturing by additive methods is very challenging. In this article, three deposition conditions are analyzed in which the energy and deposition ratio used are varied, and two cooling strategies are studied. The interpass cooling strategy (ICS) in which a fixed time is expected between passes and controlled overlay strategy (COS) in which the temperature at which the next welding pass starts is controlled. This COS strategy turns out to be advantageous from the point of view of the manufacturing time, but the deposition conditions must be correctly defined to avoid the formation of Laves phases and hot cracking in the final workpiece.

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Evolution of δ Phase Microstructure in Alloy 718

Cited by 23 publications

References 16 publications

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion

Effect of heat treatment on the microstructural evolution of a nickel-based superalloy additive-manufactured by laser powder bed fusion

Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 718

Influence of Heat Input on the Formation of Laves Phases and Hot Cracking in Plasma Arc Welding (PAW) Additive Manufacturing of Inconel 718

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