Dynamic and Post-dynamic Recrystallization During Supersolvus Forging of the New Nickel-Based Superalloy—VDM Alloy 780

Sharma, Juhi; Haghighat, M. Hafez; Gehrmann, Bodo; Moussa, Charbel; Bozzolo, Nathalie

doi:10.1007/978-3-030-51834-9_44

Cited by 8 publications

(10 citation statements)

References 23 publications

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“…The stress of these curves exhibits a further rise after yield drop until the peak stress is reached. In literature, such yield drop behavior has also been observed in other nickel-based superalloys [26,27]. Explanations for this phenomenon include the following theories: A general explanation is that after the pinning of dislocations by solute atoms a higher stress is needed to mobilize these locked dislocations [28].…”

Section: True Stress-true Strain Curvesmentioning

confidence: 78%

“…In the study of Guimaraes [29], short range ordering of γ′ forming elements (Ti and Al) as well as carbides are responsible for locking dislocations in Waspaloy in the yield stage. Sharma et al [26] attributes this effect to the decrease of stacking fault energy (SFE) due to Co and Nb elements which makes the slip of partial dislocations difficult. The yield drop phenomenon observed in the present work can be explained by almost all the above theories.…”

Section: True Stress-true Strain Curvesmentioning

confidence: 99%

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Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

Wang

Qin³

et al. 2023

Mater. Res. Express

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The deformation behavior of a new Ni-Co base superalloy GH4251 under hot compression tests within the deformation strain window of 0.36 to 1.2 was investigated in the temperature range of 1050~1170 °C and strain rate range of 0.001~1 s−1. Based on the analysis of true stress-strain curves, constitutive equations were established to describe the rheological behavior during hot compression. Microstructure evolution was investigated by transmission electron microscope (TEM), scanning electron microscope (SEM) and optical metallography (OM). The results show that flow behavior of GH4251 alloy is combinedly determined by the effect of work hardening and dynamic recrystallization (DRX). The deformation activation energies at strain of 0.36 to 1.2 are calculated to be 311~536 kJ/mol in the super-solvus temperature region, and 796~1064 kJ/mol in the sub-solvus temperature region. The recrystallization nucleation mechanism of GH4251 alloy is strain induced grain boundary migration (SIBGM). The occurrence and expansion of recrystallization are strongly promoted by high deformation temperatures and high strain rates, while the DRX grain size increases with elevated deformation temperature. When the deformation temperature is below 1090℃, the recrystallized grain can be extremely small (<17µm), which is rather independent on strain and strain rate. However, above 1110 ℃ the grain size at strain rate of 0.001s-1 is significantly larger than that of higher strain rates. The difference can be ascribed to the presence of γ’ phase, with which the development of dynamic recrystallization is postponed, while the growth of recrystallized grains is inhibited as well.

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Section: True Stress-true Strain Curvesmentioning

confidence: 78%

Section: True Stress-true Strain Curvesmentioning

confidence: 99%

Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

Wang

Qin³

et al. 2023

Mater. Res. Express

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“…The initial investigations suggested that the strain rate sensitivity in this alloy is weak and the impact of strain rate on microstructural evolution weakens with temperature. [9] Therefore, the PDRX experiments on cylinder samples were performed at only 0.1 s À1 (Figure 2(d)).…”

Section: B Hot Compression Testsmentioning

confidence: 99%

Supersolvus Recrystallization and Grain Growth Kinetics for the Fine Tuning of Grain Size in VDM Alloy 780 Forgings

Haghighat¹,

Sharma

Gehrmann³

et al. 2023

Metall Mater Trans A

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VDM Alloy 780 is a new polycrystalline nickel-based superalloy developed for aeronautical applications. In most of the targeted applications, grain size after forging must be precisely controlled to meet the targeted mechanical properties and in-service life requirements. Grain size in forgings is the direct consequence of the recrystallization and grain growth kinetics which are addressed in this paper at high temperatures, above the solvus temperature of γ′ and η/δ phases. The dynamic and post-dynamic recrystallization kinetics as well as the grain growth kinetics of VDM Alloy 780 are detailed over a range of thermomechanical conditions. Dynamic recrystallization appears to be limited, with only 30 pct recrystallized at quite high strain of 1.7 applied at 1050 °C and 0.01 s−1 for instance, but this is compensated by fast post-dynamic evolution. Within the investigated thermomechanical range, recrystallization is completed with 5 minutes of post-deformation hold in VDM Alloy 780 independent of the prior strain, strain rate and dynamic recrystallization fraction. For a strain as low as 0.08, an isothermal annealing of 30 minutes at 1050 °C generates a homogenous and fully recrystallized microstructure. Capillarity driven grain growth following recrystallization is also relatively slow, for instance an exposure at 1050 °C (50 °C above the solvus temperature) for 2 hours results in an increase in average grain size from 20 to 70 μm. This opens the possibility to fine tune the grain sizes by subsequent heat treatments within a time scale that is compatible with industrial conditions. The high cobalt content (25 pct) is suspected to play a role in the control of microstructure evolution kinetics. It is noteworthy that VDM Alloy 780 is shown here to not undergo the heterogeneous grain growth phenomenon reported in low strain regions for other nickel-based superalloys, which is also an asset for applications requiring strict control of grain sizes and grain size distributions.

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“…1 The schematic of beadon-plate weld run on the VDM Alloy 780 plates and the corresponding location where the cross-sections were cut out the AWS D17.1 M:2010. Therefore, 1.5 mm was used as the minimum acceptable value for Wm in aerospace applications as the reference [15].…”

Section: Weld Geometry and Weld Defects Quantificationmentioning

confidence: 99%

“…The center points in all responses, i.e., Sample 5-7, show reasonably similar values. This is reflected in the calculated reproducibility value of 0.940, 0.856, 0.732, 0.938, and 0.984 for Wm, face and root excess weld metal, face underfill, and diameter are compared with the maximum acceptable limit specified in AWS D17.1 M:2010, while 1.5 mm is used as the minimum acceptable limit for Wm as a reference, shown in red dotted lines [15] average pore diameter, respectively. Moreover, all the DOE runs produced welds with Wm larger than 1.5 mm and excess weld metals, face underfill, and average pore diameter lower than the maximum allowable limit stipulated in AWS D17.1 M:2010 [13] for aerospace applications.…”

Section: Influence Of K-tig Welding Process Parameters On Weld Geomet...mentioning

confidence: 99%

Keyhole TIG welding of newly developed nickel-based superalloy VDM Alloy 780

et al. 2022

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The influence of keyhole TIG (K-TIG) welding parameters on the weld geometry and defects of a new nickel-based superalloy VDM Alloy 780 alloy were investigated using a statistical design of experiment, and the microstructures of the heat-affected zone (HAZ) and fusion zone (FZ) of the K-TIG-welded VDM Alloy 780 were characterized. No cracks are found in the FZ and HAZ. Travel speed significantly influences the minimum weld width (Wm), face and root excess weld metal, face underfill, and average pore diameter. Welding current and the interaction current*travel speed significantly influence the face and root excess weld metals, respectively. Interdendritic microconstituents in the FZ are identified as (Nb,Ti)C particles and γ/Laves eutectic constituents based on SEM–EDS analysis. In addition, plate-like precipitates likely to be δ/η phase are observed surrounding the interdendritic Laves eutectics, and γ′ precipitates are found to be inhomogeneously precipitated in the FZ. In the partially melted zone (PMZ), (Nb,Ti)C, Laves phase, and plate-like particles are found in the liquated and resolidified regions. Constitutional liquation of (Nb,Ti)C in HAZ is observed where the liquated (Nb,Ti)C appears to be associated with the γ/Laves eutectic as a resolidified product.

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Dynamic and Post-dynamic Recrystallization During Supersolvus Forging of the New Nickel-Based Superalloy—VDM Alloy 780

Cited by 8 publications

References 23 publications

Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

Supersolvus Recrystallization and Grain Growth Kinetics for the Fine Tuning of Grain Size in VDM Alloy 780 Forgings

Keyhole TIG welding of newly developed nickel-based superalloy VDM Alloy 780

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