Elemental site occupancy in the L12 A3B ordered intermetallic phase in Co-based superalloys and its influence on the microstructure

Pandey, Prafull; Makineni, Surendra Kumar; Samanta, Atanu; Sharma, Ankit; Das, Sourav; Baler, Nithin; Srivastava, Chandan; Singh, Abhishek K.; Raabe, Dierk; Gault, Baptiste; Chattopadhyay, K.

doi:10.1016/j.actamat.2018.09.049

“…It was suggested that the decrease in the partitioning coefficient of bigger sized W element in the γ phase [25,44] with substitution of larger W/Ta atoms with comparatively smaller Cr atoms resulted in a contraction of the γ phase, while partitioning of Cr resulted in an expansion of the γ matrix. A similar effect of Cr addition was observed in the W free Co-based superalloys where subsequent addition of Cr resulted in partitioning reversal of Mo from the dominating presence in γ phase to equal in both the phases to the γ phase [22].…”

Section: Change In Partitioning Behaviour With Cr Additionsupporting

confidence: 64%

“…The liquidus temperature is above 1350°C in all three alloys, and therefore could not be captured experimentally due to experimental limitation. The γ solvus temperature and mass density of the studied alloys are plotted and compared with other superalloys [21][22][23][24][25][26] in Figure 2(c). The replacement of Co (8.90 g/cc) with lighter Cr (7.19 g/cc) marginally decreases the mass density from 8.27 g/cc for the CCA-2Cr alloy to 8.23 g/cc for the CCA-8Cr alloy.…”

Section: Thermophysical Propertiesmentioning

confidence: 99%

Effect of Cr addition on the γ′ strengthened CoNiCrAlMo compositionally complex alloy

Pandey

¹

,

Pantawane

²

,

Baler

³

et al. 2023

Materials Science and Technology

3

0

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The present study illustrates the effect of varying Cr content in Co51- xNi30Al10Mo5Nb2Ti2Cr x ( x = 2, 5, and 8 at.-%) compositionally complex alloys (CCAs). STEM-EDS analysis suggests a change in Mo partitioning from equal in both the phases (γ and γ′) in CCA-2Cr to the γ phase in CCA-5Cr and CCA-8Cr alloys. This peculiar compositional partitioning with Cr content beyond 2% brings a change in γ′ precipitate morphology from cuboidal to spheroidal in CCAs. The shape change-induced reduction in strain energy rendered a decrease in γ′ coarsening rate by ∼ 1/2, i.e. from 11.5 to 4.6 nm3/s in the CCA-2Cr and CCA-8Cr alloys, respectively. All three alloys show an anomalous increase in 0.2% proof stress (PS) with temperature and achieve peak values at 770°C.

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“…However, we observe a reverse partitioning of Mo i. [6,72,74], it is safe to assume that the larger intensity peak at lower 2q value corresponds to g' precipitates with a higher volume fraction and smaller intensity peak at higher 2q value corresponds to the γ matrix. The constrained bulk lattice misfit between g¢ and g was calculated by the formula…”

Section: Compositional Partitioning Across the G/g¢ Interface For The...mentioning

confidence: 61%

“…The peak intensities cannot be compared quantitatively with the volume fraction of phases due to possible influences of other factors such as ordering parameters and texture component. However, due to known positive lattice misfit in the Co-based superalloys [6,72,74], it is safe to assume that the larger intensity peak at lower 2q value corresponds to g' precipitates with a higher volume fraction and smaller intensity peak at higher 2q value corresponds to the γ matrix. The constrained bulk lattice misfit between g¢ and g was calculated by the formula…”

Section: Evaluation Of Lattice Mismatch Across G/g¢ Interfacementioning

confidence: 99%

On the Effect of Re Addition on Microstructural Evolution of a CoNi-Based Superalloy

Pandey

¹

,

Sawant

²

,

Baler

³

et al. 2018

SSRN Journal

0

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In this study, the effect of rhenium (Re) addition on microstructural evolution of a new low-density Co-Ni-Al-Mo-Nb based superalloy is presented. Addition of Re significantly influences the γ' precipitate morphology, the γ/γ' lattice misfit and the γ/γ' microstructural stability during long termaging. An addition of 2 at.% Re to a Co-30Ni-10Al-5Mo-2Nb (all in at.%) alloy, aged at 900°C for 50 hours, reduces the γ/γ' lattice misfit by ~ 40% (from +0.32% to +0.19%, measured at room temperature) and hence alters the g' morphology from cuboidal to round-cornered cuboidal precipitates. The composition profiles across the γ/γ' interface by atom probe tomography (APT) reveals Re partitions to the g phase ( "# = 0.34) and also results in the partitioning reversal of Mo to the g phase ( *+ = 0.90) from the γ' precipitate. An inhomogeneous distribution of Gibbsian interfacial excess for the solute Re (Γ "# , ranging from 0.8 to 9.6 atom.nm -2 ) has been observed at the γ/γ' interface. A coarsening study at 900°C (up to 1000 hours) suggests that the coarsening of γ' precipitates occurs solely by an evaporation-condensation (EC) mechanism. This is contrary to that observed in the Co-30Ni-10Al-5Mo-2Nb alloy as well as in some of the Ni-Al based and high mass density Co-Al-W based superalloys, where γ' precipitates coarsen by coagulation/coalescence mechanism with extensive alignment of γ' along <100> directions as a sign of microstructural instability. The γ' coarsening rate exponent ( / ) and γ/γ' interfacial energy are estimated to be 1.41 ´ 10 -27 m 3 /s and 8.4 mJ/m 2 , which are comparable and lower than Co-Al-W based superalloys.Keywords: Rhenium (Re); Cobalt-based superalloys; Lattice misfit; Atom probe tomography (APT); Coarsening kinetics. all transition metals in fcc-Co [56]. Due to the higher vacancy formation energy in Co, the diffusivity and activation energy barrier of Re is greater than Ni [56,57]. However, Kolb et al. [54] and Volz et al. [55] showed Re addition to a single crystalline Co-Ni-Al-W based alloy leads to a marginal or no improvement in creep properties compared to the role of Re in the 2 nd and 3 rd generation Ni-Al based superalloys. This was attributed to the low partitioning of Re to the γ matrix phase. Hence, it was concluded that Re is not crucial for Co-Al-W based superalloys.The addition of Re could have an important role for the long term microstructural stability of Co-Al based superalloys. However, the role of Re in the coarsening behavior of cobalt based alloys, in particular that of the low-density Co-Al-Mo-Nb/Ta based superalloys, has not been explored rigorously. Some studies on the kinetics and associated models have been reported for Re added Ni-Al based superalloys [27,28,58]. They show that the coarsening of precipitates follows Lifshitz-Slyozov-Wagner (LSW) based Ostwald ripening mechanism with slight variation in temporal exponents.The present work reports a detailed study on the effect of Re addition on a low density W-free g/g¢ Co-Al based superalloys. Microstructural evolut...

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“…The peak intensities cannot be compared quantitatively with the volume fraction of phases due to possible influences of other factors such as ordering parameters and texture component. However, due to known positive lattice misfit in the Co-based superalloys [6,72,74], it is safe to assume that the larger intensity peak at lower 2q value corresponds to g 0 precipitates with a higher volume fraction and smaller intensity peak at higher 2q value corresponds to the g matrix. The constrained bulk lattice misfit between g 0 and g was calculated by the formula…”

Section: 12mentioning

confidence: 99%

On the effect of Re addition on microstructural evolution of a CoNi-based superalloy

Pandey

¹

,

Sawant

²

,

Baler

³

et al. 2019

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In this study, the effect of rhenium (Re) addition on microstructural evolution of a new low-density Co-Ni-Al-Mo-Nb based superalloy is presented. Addition of Re significantly influences the g 0 precipitate morphology, the g/g 0 lattice misfit and the g/g 0 microstructural stability during long term aging. An addition of 2 at.% Re to a Co-30Ni-10Al-5Mo-2Nb (all in at.%) alloy, aged at 900 C for 50 h, reduces the g/ g 0 lattice misfit by~40% (from þ0.32% to þ0.19%, measured at room temperature) and hence alters the g 0 morphology from cuboidal to round-cornered cuboidal precipitates. The composition profiles across the g/g 0 interface by atom probe tomography (APT) reveal Re partitions to the g phase (K Re ¼ 0:34Þ and also results in the partitioning reversal of Mo to the g phase (K Mo ¼ 0:90) from the g 0 precipitate. An inhomogeneous distribution of Gibbsian interfacial excess for the solute Re (G Re , ranging from 0.8 to 9.6 atom.nm À2) has been observed at the g/g 0 interface. A coarsening study at 900 C (up to 1000 h) suggests that the coarsening of g 0 precipitates occurs solely by evaporationecondensation (EC) mechanism. This is contrary to that observed in the Co-30Ni-10Al-5Mo-2Nb alloy as well as in some of the Ni-Al based and high mass density CoAl -W based superalloys, where g 0 precipitates coarsen by coagulation/coalescence mechanism with an extensive alignment of g 0 along <100> directions as a sign of microstructural instability. The g 0 coarsening rate constant ðK r Þ and g/g 0 interfacial energy are estimated to be 1.13 Â 10 À27 m 3 /s and 8.4 mJ/m 2 , which are comparable and lower than CoAl -W based superalloys.

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Elemental site occupancy in the L12 A3B ordered intermetallic phase in Co-based superalloys and its influence on the microstructure

Cited by 77 publications

References 76 publications

Effect of Cr addition on the γ′ strengthened CoNiCrAlMo compositionally complex alloy

Effect of Cr addition on the γ′ strengthened CoNiCrAlMo compositionally complex alloy

On the Effect of Re Addition on Microstructural Evolution of a CoNi-Based Superalloy

On the effect of Re addition on microstructural evolution of a CoNi-based superalloy

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