Hydrogen embrittlement in nickel-based superalloy 718: Relationship between γ′ + γ″ precipitation and the fracture mode

Rezende, Mônica Costa; Araújo, Leonardo Sales; Gabriel, Sinara Borborema; Santos, D.S. dos; Almeida, Luiz Henrique de

doi:10.1016/j.ijhydene.2015.07.053

Cited by 70 publications

(15 citation statements)

References 30 publications

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“…and small (secondary) g¢¢ precipitates. Similar bi-modal g¢¢ precipitate distributions were observed by Rezende et al [18] and Miller et al [19] . SC-aged samples also showed evidence of g¢¢ precipitate free zones near grain boundaries with more δ phase formation, see inset of Figure 3d.…”

Section: Microstructural Evolutionsupporting

confidence: 85%

Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Obasi

Zhang

Sampath

et al. 2018

Metall Mater Trans A

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The sensitivity to hydrogen embrittlement (HE) has been studied in respect to precipitation size distributions in two nickel base superalloys, Alloy 718 (UNS N07718) and Alloy 945X (UNS N09946). Quantitative microstructure analysis was carried out by the combination of scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy (EDS). While Alloy 718 is mainly strengthened by g¢¢, and therefore readily forms reduced sensitivity to HE compared to Alloy 718 when considering high strength conditions despite the absence of intergranular d phase.

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Section: Microstructural Evolutionsupporting

confidence: 85%

Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Obasi

Zhang

Sampath

et al. 2018

Metall Mater Trans A

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“…Thus, except from providing remarkable strength to the subsea bolt, the exact effect of metastable γ" on HE surface cracking remains unclear. However, solution-annealed specimens S1 and S3 only contain MCN particles, and Rezende et al [8] have reported that for solution-annealed specimens, the HE im- In this study, twin boundaries were also observed for all 718 variants, including bolt specimens S6 and S7, as seen in Figure 9. Some researchers have reported [45] [46] that twin boundaries are considered to have low hydrogen solubility and high separation energy, which makes them less susceptible to HE.…”

Section: Discussionsupporting

confidence: 51%

“…Typically, the subsea bolts of Inconel family are cold rolled and, then, heat-treated; however, this process results in an increase in the localized hardness, lower ductility, discrete grain boundary precipitation, and higher susceptibility to HE [2]. The reason for this abrupt change in mechanical and corrosive properties is attributed to the microstructure where the detrimental role of intergranular precipitates for HE has already been well established [2] [8] [9] [10] [11], and the analysis of 718 service failures has been performed by Cassagne et al [12]. Moreover, phase kinetic simulations [13] [14] defined the alloy 718 limitations, which led to the development of controlled microstructure for specific applications [1] [7].…”

Section: Background Problemmentioning

confidence: 99%

Alloy 718 Subsea Bolt in Relation to Surface Cracking: A Microstructural Perspective

Saleem¹,

Dong²,

Patel³

2020

MSA

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The brittle fracture mode close to the surface of Inconel 718 subsea bolts is closely related to their nanostructure. When the bolts are used subsea under cathodic protection, hydrogen evolves. Intergranular precipitates and points of intersection of slip lines always held responsible for hydrogen enhanced decohesion. However, thus far, little attention has been paid to the bolts manufacturing method and to the characterization of the role of subsurface oversized nanoprecipitates on transgranular surface cracking. As-received subsea bolts were analyzed using multi-scale observation techniques such as focused ion beam milling, scanning electron microscopy, transmission electron microscopy, and in-air strain rate tensile tests. The results further demonstrated that under identical API aging, there was a difference in the morphological precipitation and strength of 718 as a bolt and rectangular billet. For the 718 rectangular billets, discrete intergranular stable δ/MC carbides precipitate and only γ' of 10-20 nm was observed for the bulk and subsurface. Whereas, for the CRA subsea bolt, γ' was approximately 30 nm, γ" was 30-50 nm for the bulk (370 HV); γ' was approximately 50 nm and γ" was 50-100 nm at subsurface (400 HV). As-received subsea bolts were investigated at subsurface (10 µm from the surface) at the thread and shank region, which revealed transgranular sheared oversized ~50 nm γ' (with dislocation networks) and metastable γ" > 100 nm particles, respectively. Thus, an effort was made to develop the hydrogen-assisted surface cracking theory for bolts.

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“…Alloy 718 is often susceptible to intergranular failures of different nature, such as oxygen assisted intergranular cracking (OAIC) and hydrogen embrittlement 12,13 . Hence, some authors propose the deliberated manipulation of grain boundary character distribution (GBCD) in order to mitigate those phenomena by breaking the connectivity of random high angle boundaries, more prone to crack propagation 14,15 .…”

Section: Introductionmentioning

confidence: 99%

Effects of Different Wire Drawing Routes on Grain Boundary Character Distribution, Microtexture, δ-Phase Precipitation, Grain Size and Room Temperature Mechanical Behavior of Alloy 718

et al. 2020

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Over the last decades, alloy 718 usage has expanded and requirements imposed by its industrial applications became more critical. The knowledge about grain boundary character distribution (GBCD) in alloy 718 and its effect on properties improvement is mostly built based on iterative processing through cold rolling steps interspersed with solution annealing. Alloy 718 is found in the industry in many different forms and geometries, and fabricated by multiple thermomechanical processes such as wire drawing, rolling, forging or extrusion. The present study focused on understanding how wires respond to deformation mode related to drawing in regard to GBCD evolution, crystallographic orientation, precipitation of δ-phase and grain size. Lastly, assessing the resulting mechanical properties. The findings show that microstructural evolution is a consequence of competing mechanisms such as strain induced boundary migration, recrystallization, grain growth and phase precipitation. The deformation gradient along wire cross section plays an important role in affecting microstructural features, such as δ precipitation, GBCD and microtexture.

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Hydrogen embrittlement in nickel-based superalloy 718: Relationship between γ′ + γ″ precipitation and the fracture mode

Cited by 70 publications

References 30 publications

Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

Alloy 718 Subsea Bolt in Relation to Surface Cracking: A Microstructural Perspective

Effects of Different Wire Drawing Routes on Grain Boundary Character Distribution, Microtexture, δ-Phase Precipitation, Grain Size and Room Temperature Mechanical Behavior of Alloy 718

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