A new tungsten-free γ–γ’ Co–Al–Mo–Nb-based superalloy

Makineni, Surendra Kumar; Baler, Nithin; Chattopadhyay, K.

doi:10.1016/j.scriptamat.2014.11.009

Cited by 157 publications

(68 citation statements)

References 29 publications

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“…Given that the L1 2 γ phase can be attained in the Ni-Al, CoAl-W, Co-Al-Mo-Nb [42] and Co-Al-Mo-Ta systems [43], characterisation of the complex bonding energetics is also of great importance. Through a unified understanding of the compositional effects on the gradient energy, the interfacial strain energy arising from the lattice misfit, as well as the combined effect that these two properties have on the dislocation-interface interactions, optimal interfacial characteristics can be engineered.…”

Section: Discussionmentioning

confidence: 99%

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Vorontsov¹,

Barnard

Rahman³

et al. 2016

Acta Materialia

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This work discusses the effects of alloying on the coarsening behaviour of the L1 2 ordered γ phase and the structure of the γ/γ interfaces in three Co-Al-W base superalloys aged at ∼90 • C below the respective solvus temperatures: Co-7Al-7W, Co10Al-5W-2Ta and Co-7Al-7W-20Ni (at.%). The coarsening kinetics are adequately characterised by the classical Lifshitz-Slyozov-Wagner model for Ostwald ripening. Co-7Al-7W exhibited much slower coarsening than its quaternary derivatives. Alloying can be exploited to modify the coarsening kinetics either by increasing the solvus temperature by adding tantalum, or by adding nickel to shift the rate controlling mechanism towards dependence on the diffusion of aluminium rather than tungsten. Lattice resolution STEM imaging was used to measure the widths of the order-disorder (structural) and Z-contrast (compositional) gradients across the γ/γ interfaces. Similarly to nickel base superalloys, the compositional gradient was found to be wider than the structural. Co-7Al-7W-20Ni had much wider interface gradients than Co-7Al-7W and Co-10Al-5W-2Ta, which suggests that its γ phase stoichiometry is less constrained. A possible correlation between temperature and misfit normalised r vs. t 1 3 coarsening rate coefficients and the structural gradient width has also been identified, whereby alloys with wider interfaces exhibit faster coarsening rates.

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Section: Discussionmentioning

confidence: 99%

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Vorontsov¹,

Barnard

Rahman³

et al. 2016

Acta Materialia

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“…Mo is element promoting c¢ formation and hence may replace tungsten in Co-based superalloys. In 2015 occurred the first data concerning new W-free c-c¢ Co-Al-MoNb Co-based superalloys (Ref 3,25,26). The density of Nbcontaining superalloys was 8.25-8.355 g cm À3 , therefore definitely lower compared to that of Co-7W-7Al alloy (at.%), characterized by density equal 9.2 g cm À3 .…”

Section: This Challenge Has Been Taken In 2006 By Sato Et Al (Ref 8)mentioning

confidence: 99%

Surface Condition of New γ–γ′ Co-Al-Mo-Nb and Co-Al-W Cobalt-Based Superalloys After Oxidation at 800 °C

Migas

Moskal

Niemiec

2018

J. of Materi Eng and Perform

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A new type c-c¢ Co-Al-Mo-Nb Co-based superalloys were developed due to limitations of basic Co-Al-W superalloys, related to tungsten alloying. The present study aims to characterization of new c-c¢ Co-10Al-5Mo-2Nb (at.%) cobalt-based superalloy performance in terms of the high-temperature exposure under cyclic conditions, with particular regard to surface condition. Specimens were tested in cycles of hightemperature exposition (25, 50, 75, 100 and 150 h) in air environment at 800°C. Detailed analysis of oxidized surfaces by scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction was made at various intervals during testing. The cyclic oxidation behavior of new alloy was compared to the basic Co-9Al-9W (at.%) Co-based superalloy.

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“…0 cobalt superalloys based on Co-Al-Mo-Nb/Ta system that does not contain W have opened up new possibilities in designing high-temperature alloys with lower densities [34][35][36]. The c-c 0 microstructure is stabilized in these alloys by a small addition of Nb or Ta.…”

Section: Recent Reports On New C-cmentioning

confidence: 99%

“…The lattice misfit at the interface depends on the relative chemistry across the interface and atomic sizes of the constituent elements in both c matrix and c 0 precipitate. The alloys that do not contain Cr exhibits L1 2 ordered precipitates with cuboidal morphology [34]. Hence, with the variation of Cr content in these alloys, the lattice misfit at the c/c 0 interface can be modulated or controlled.…”

Section: Ab Initio Calculationsmentioning

confidence: 99%

“…For comparison of the values with the alloys that do not contain Cr, the compositions of c and c 0 for Co-30Ni-10Al-5Mo-2Ta (2Ta) and Co-30Ni-10Al-5Mo-2Ta-2Ti (2Ta2Ti) alloys taken from the Ref. [34] were also included. The partitioning coefficient (K) is calculated by the formula K = C c 0 /C c (where C c 0 and C c are concentration of the element in the ordered c 0 precipitate and matrix c phase, respectively).…”

Section: Ab Initio Calculationsmentioning

confidence: 99%

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Effect of Cr addition on γ–γ′ cobalt-based Co–Mo–Al–Ta class of superalloys: a combined experimental and computational study

et al. 2017

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The present article deals with effect of Cr addition (10 at.%) on the partitioning behavior and the consequent effect on mechanical properties for tungsten-free c-c 0 cobalt-based superalloys with base alloy compositions of Co-30Ni-10Al-5Mo-2Ta (2Ta) and Co-30Ni-10Al-5Mo-2Ta-2Ti (2Ta2Ti). Cr addition leads to a change in the morphology of the strengthening cuboidal-shaped c 0 precipitates to a spherical shape. The site preference of Cr atoms in two alloy systems (with and without Ti) has been experimentally investigated using atom probe tomography with the supportive prediction from first principles DFT-based computations. Cr partitions more to the c matrix relative to c 0 . However, Cr also has a strong effect on the Ta and Mo partitioning coefficient across c/c 0 interfaces. The value of partition coefficient for Mo (K Mo ) becomes \1 with Cr addition to the alloys. Results from ab initio calculations show that the Cr atoms prefer to replace Mo atoms in the sublattice sites of the L1 2 unit cell. The solvus temperature of about 1038 and 1078°C was measured for 10Cr2Ta and 10Cr2Ta2Ti alloy, respectively, and these Cr-containing alloys have very low densities in the range of *8.4-8.5 gm/cm -3 . The 0.2% compressive proof strength of 10Cr2Ta2Ti alloy yields a value of 720 MPa at 870°C, substantially better than most Co-Al-W-based alloys and many of the nickel-based superalloys (e.g., MAR-M-247).

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A new tungsten-free γ–γ’ Co–Al–Mo–Nb-based superalloy

Cited by 157 publications

References 29 publications

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Surface Condition of New γ–γ′ Co-Al-Mo-Nb and Co-Al-W Cobalt-Based Superalloys After Oxidation at 800 °C

Effect of Cr addition on γ–γ′ cobalt-based Co–Mo–Al–Ta class of superalloys: a combined experimental and computational study

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