Lower temperature deformation mechanisms in a γ″-strengthened Ni-base superalloy

McAllister, Donald; Lv, Duchao; Peterson, Benjamin; Deutchman, H.; Wang, Y.; Mills, Michael J.

doi:10.1016/j.scriptamat.2015.11.026

Cited by 33 publications

(13 citation statements)

References 14 publications

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“…For example, the planar fault traversing from the bottom left to the top right of the micrograph shows isolated faulted coprecipitates. Isolated faults have been frequently reported for air-cooled IN718 containing non-compact coprecipitates, deformed under similar conditions [19][20][21][22][23]. Further, across this micrograph, several dislocation loop/debris like features are visible.…”

Section: Discussionsupporting

confidence: 68%

Creep Behavior of Compact γ′-γ″ Coprecipitation Strengthened IN718-Variant Superalloy

Mukopadhyay

Sriram

Zenk

et al. 2021

Metals

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The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.

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Section: Discussionsupporting

confidence: 68%

Creep Behavior of Compact γ′-γ″ Coprecipitation Strengthened IN718-Variant Superalloy

Mukopadhyay

Sriram

Zenk

et al. 2021

Metals

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“…The presence of c¢¢ precipitates has been associated with coherency hardening 44,45 where the dislocations cut through the precipitates, introducing stacking faults and antiphase boundaries in the precipitates. 46,47 The presence of d phase has been shown to inhibit the dislocation movement during deformation 48 , 49 and dislocations pile up in the vicinity of the precipitates, which act as breakable pins. With increasing stress, energetic dislocation avalanches occur as they overcome the precipitates, thus giving rise to strong AE signals.…”

Section: Resultsmentioning

confidence: 99%

The Effect of γ″ and δ Phase Precipitation on the Mechanical Properties of Inconel 718 Manufactured by Selective Laser Melting: An In Situ Neutron Diffraction and Acoustic Emission Study

Čapek

Polatidis

Knapek

et al. 2020

JOM

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The deformation behavior of additively manufactured Alloy 718 in as-built condition and after annealing was studied in situ under tensile loading along the build direction. Pre-characterization by synchrotron X-ray diffraction and electron microscopy revealed a significant amount of γ″ precipitates in the as-built samples, whereas the γ″ phase was entirely consumed and needle-like δ precipitates appeared in the annealed sample. In situ neutron diffraction (ND) and acoustic emission (AE) enabled indirect observation of the role of the precipitates on the mechanical behavior. ND provided information on the load accommodation in the matrix, while AE detected a strong signal from the interaction of dislocations with the δ-phase precipitates during deformation of the annealed samples. The results imply that in the annealed samples the matrix sheds the load to the precipitates, while in the as-built material the matrix bares a significant load.

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“…Therefore, it is proposed that g¢ -matrix interfaces serve as preferential nucleation sites for g″ [28], because the lattice strain energy caused by g″ nucleating on g¢ -matrix interfaces is lower than that of g″ nucleating completely within the matrix [23,32,33]. Coprecipitates have been shown to improve mechanical responses by requiring more complex dislocation structures to induce plastic deformation [34,35]. They also enhance thermal stability as their coarsening rates at elevated temperatures are lower than the monolithic precipitates due to a combination of interface-controlled kinetics (i.e.…”

Section: Structure-property Relationshipsmentioning

confidence: 99%

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Gallmeyer

Moorthy

Kappes

et al. 2020

Additive Manufacturing

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Dislocation structures, chemical segregation, γ′, γ″, ! precipitates and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure is revealed. Knowledge derived from these process-structure-property relationships was used to engineer a super-solvus solution anneal at 1020 ºC for 15 minutes, followed by aging at 720 ºC for 24 hours heat treatment for AM-IN718 that eliminates Laves and δ phases, preserves AM-specific dislocation cells that are shown to be stabilized by MC carbide particles, and precipitates dense γ′ and γ″ nanoparticle populations. This "optimized for AM-IN718 heat treatment" results in superior properties relative to wrought/additively manufactured, then industry standard heat treated IN718: relative increases of 7/10% in yield strength, 2/7% in ultimate strength, and 23/57% in elongation to failure are realized, respectively, regardless of as-built vs. machined surface finishes.

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Lower temperature deformation mechanisms in a γ″-strengthened Ni-base superalloy

Cited by 33 publications

References 14 publications

Creep Behavior of Compact γ′-γ″ Coprecipitation Strengthened IN718-Variant Superalloy

Creep Behavior of Compact γ′-γ″ Coprecipitation Strengthened IN718-Variant Superalloy

The Effect of γ″ and δ Phase Precipitation on the Mechanical Properties of Inconel 718 Manufactured by Selective Laser Melting: An In Situ Neutron Diffraction and Acoustic Emission Study

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

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