Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

Bi, Zhongnan; Dong, Jie; Zhang, Maicang; Liu, Zheng; Xie, Xiangyu

doi:10.1007/s12613-010-0310-z

Cited by 32 publications

(5 citation statements)

References 13 publications

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“…12h). The formation of α-Cr on advancing δ phase has been demonstrated in IN718 after a long term ageing treatment [22][23][24][25]. Large needle γ″ in the complex constituent are also precipitated from the γ phase during post deposition ageing treatment.…”

Section: Discussionmentioning

confidence: 99%

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Electron microscopy study of direct laser deposited IN718

Ding

Huang

et al. 2015

Materials Characterization

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a b s t r a c tThe microstructure of direct laser deposited (DLD) IN718 has been investigated in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results confirm that the dendrite core microstructure can be linked to the cooling rate experienced during the deposition. A~100 μm wide δ partially dissolved region in the IN718 substrate was observed close to the substrate/deposit boundary. In the deposited IN718, γ/Laves eutectic constituent is the predominant minor microconstituent. Irregular and regular (small) (Nb,Ti)C carbides and a mixture of the carbides and Laves were observed. Most M 3 B 2 borides were nucleated around a (Nb,Ti)C carbide. Needles of δ phase precipitated from the Laves phase were also observed. A complex constituent (of Laves, δ, α-Cr, γ″, and γ matrix) is reported in IN718 for the first time. The formation of α-Cr particles could be related to Cr rejection during the formation and growth of Cr-depleted δ phase.

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Section: Discussionmentioning

confidence: 99%

“…This could be related to the fact that the δ phase is Cr-depleted, thus Cr is rejected from the δ phase during its formation and growth. The nucleation and growth of α-Cr on the surface of an advancing δ phase have been demonstrated in IN718 aged for a long time [22][23][24][25][26] and in a shorter time under stress [27].…”

Section: Complex Constituentmentioning

confidence: 99%

Electron microscopy study of direct laser deposited IN718

Ding

Huang

et al. 2015

Materials Characterization

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“…Bi et al [36] suggested that the precipitation of α-Cr phase in Inconel 718 is strongly associated with the growth of the δ phase during which a continued rejection of Cr occurs, leading to Cr segregation in the vicinity of the δ particles. It explains the observation that most Cr precipitates formed beneath the broached surface during thermal exposure were adjacent to the δ phase, see Fig.…”

Section: α-Cr Precipitationmentioning

confidence: 99%

Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures

Chen

Peng

Avdovic³

et al. 2016

Metall Mater Trans A

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The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K and 923 K (450 ˚C, 550 ˚C and 650 ˚C) for 30, 300 and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and α-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.

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“…Although it is found that α-Cr formation is associated with δ (Ni 3 Nb) phase formation due to Cr enrichment, which is caused by Ni, Al or Nb depletion from the matrix [22,23], α-Cr phase was formed in the ST alloy without the δ (Ni 3 Nb) phase following thermal exposure at 750°C…”

Section: Discussionmentioning

confidence: 99%