Creep behaviour of Ni-base single-crystal superalloys with various γ′ volume fraction

Murakumo, T.; Kobayashi, Toshiharu; Koizumi, Yutaka; Harada, Hiroshi

doi:10.1016/j.actamat.2004.04.028

Cited by 485 publications

(176 citation statements)

References 11 publications

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“…They are manufactured in polycrystalline form for turbine disks and in single crystal form for turbine airfoils. In both cases, the high strength of the alloy is due to the precipitation of a L1 2 -ordered phase phase, known as γ′, within the Nickel fcc matrix [3]. Defects such as vacancies and impurities are also thought to affect dislocation motion, and the inclusion of chemical impurities such as Re and/or W in the γ matrix is a standard commercial practice known to be extremely important to improve the plasticity response.…”

Section: Introductionmentioning

confidence: 99%

Modelling defects in Ni–Al with EAM and DFT calculations

Bianchini

Kermode

Vita

2016

Modelling Simul. Mater. Sci. Eng.

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We present detailed comparisons between the results of embedded atom model (EAM) and density functional theory (DFT) calculations on defected Ni alloy systems. We find that the EAM interatomic potentials reproduce low-temperature structural properties in both the γ and γ′ phases, and yield accurate atomic forces in bulk-like configurations even at temperatures as high as ∼1200 K. However, they fail to describe more complex chemical bonding, in configurations including defects such as vacancies or dislocations, for which we observe significant deviations between the EAM and DFT forces, suggesting that derived properties such as (free) energy barriers to vacancy migration and dislocation glide may also be inaccurate. Testing against full DFT calculations further reveals that these deviations have a local character, and are typically severe only up to the first or second neighbours of the defect. This suggests that a QM/MM approach can be used to accurately reproduce QM observables, fully exploiting the EAM potential efficiency in the MM zone. This approach could be easily extended to ternary systems for which developing a reliable and fully transferable EAM parameterisation would be extremely challenging e.g. Ni alloy model systems with a W or Re-containing QM zone.

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Section: Introductionmentioning

confidence: 99%

Modelling defects in Ni–Al with EAM and DFT calculations

Bianchini

Kermode

Vita

2016

Modelling Simul. Mater. Sci. Eng.

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“…Further reasons might be the substantially higher γ'-solvus temperature and the increased γ'-volume fraction of 82 %, compared to 58 % of alloy 9W-B (Table 1). However, both γ'-volume fractions differ from 70 % which is found to be the optimum for γ/γ'-Ni-base superalloys [31]. In contrast, the alloy 9W-2Ti-0.12B exhibits a γ'-volume fraction of 75 %, which might be one reason for the superior creep strength among the investigated Co-base alloys [14].…”

Section: Misfit Measurementsmentioning

confidence: 65%

Creep Strength and Microstructure of Polycrystalline γ' - Strengthened Cobalt-base Superalloys

Bauer¹,

Neumeier²,

Pyczak³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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The influence of several alloying elements on the microstructure and creep properties of polycrystalline Co-base superalloys hardened with the ternary L1 2 compound, γ'-Co 3 (Al,W), are presented in this work. The stability of the γ/γ'-microstructure was investigated by long term aging at temperatures of 750 °C and 900 °C. High contents of chromium and iron destabilize the γ/γ'-microstructure. Additions of nickel widen the γ/γ'-two phase field. Discontinuous precipitation is observed only in the iridiumcontaining alloy during aging. In all other alloys no formation of further intermetallic phases are found even after 1000 hrs aging at 750 °C and 900 °C. Boron has been added for the formation of grain boundary strengthening intermetallic phases which leads to an adjacent γ'-depleted zone. Nanoindentation shows that titanium improves its hardness. The creep strength of the studied alloys is sufficiently better than that of commercial carbide hardened polycrystalline Co-base superalloys and already close to γ'-hardened Ni-base superalloys. An alloy containing 2 at.% titanium exhibited a creep strength comparable with the Ni-base alloy IN100. The microstructure after creep tests at 950 °C showed rafting perpendicular to the compressive load axis, confirming the positive lattice misfit of the alloys at high temperatures which was determined with high energy X-ray diffraction.

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“…2 is a term that corresponds to the optimal value of V f , which is the value reported by Murakumo et al [16]. They found that creep-rupture lives are the longest at around 0.7 and 0.55 of the measured ' volume fraction at 900 ºC/392 MPa and 1100 ºC/137 MPa, respectively, using TMS-75 and its γ/' tie-line alloys.…”

Section: Resultsmentioning

confidence: 99%

Quantitative Analysis of Creep Strengthening Factors in Ni-base Single Crystal Superalloys

Yokokawa¹,

Harada²,

Kawagishi³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Ni-base single-crystal (SC) superalloys with superior mechanical properties are being developed to improve the thermal efficiency of jet engines and land-based gas turbines. In this study, we investigate the relationships among alloy compositional factors, structural factors, and the creep-rupture life of Ni-base SC superalloys by multi-regression analysis with creep-tested data for 75 alloys. We also obtain three equations to predict creep-rupture lives at 900 ºC/392 MPa, 1000 ºC/245 MPa, and 1100 ºC/137 MPa with excellent multi-correlation coefficients from 0.94 to 0.98. The ' phase composition, ' volume fraction, and lattice misfit were used as explanatory variables. The regression coefficients of the refractory elements including W, Ta, and Re were comparatively large at 900 ºC/392 MPa and they decreased with an increase in temperature and decrease in stress. The coefficient for negative lattice misfit increased at higher temperatures and lower stresses, especially at 1100 ºC/137 MPa. The coefficient of Ru showed a small value for all the conditions in this study. Consequently, it is clear that solution strengthening is effective in the lower-temperature and higher-stress regions, and that a larger negative misfit leads to a quicker formation of the rafted /' structure with a finer interfacial dislocation network. The finer dislocation network assures superior creep resistance by preventing glide dislocation from cutting the rafted /' structure. The addition of Ru in alloys is effective in suppressing topologically close packed (TCP) phases formation by expanding the solubility limit. The lattice misfit shifts toward a slightly negative value with the addition of Ru, but this effect was small with respect to the enhancement of creep strength.

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Creep behaviour of Ni-base single-crystal superalloys with various γ′ volume fraction

Cited by 485 publications

References 11 publications

Modelling defects in Ni–Al with EAM and DFT calculations

Modelling defects in Ni–Al with EAM and DFT calculations

Creep Strength and Microstructure of Polycrystalline γ' - Strengthened Cobalt-base Superalloys

Quantitative Analysis of Creep Strengthening Factors in Ni-base Single Crystal Superalloys

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Creep behaviour of Ni-base single-crystal superalloys with various γ′ volume fraction

Cited by 485 publications

References 11 publications

Modelling defects in Ni–Al with EAM and DFT calculations

Modelling defects in Ni–Al with EAM and DFT calculations

Creep Strength and Microstructure of Polycrystalline &gamma;' - Strengthened Cobalt-base Superalloys

Quantitative Analysis of Creep Strengthening Factors in Ni-base Single Crystal Superalloys

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Creep Strength and Microstructure of Polycrystalline γ' - Strengthened Cobalt-base Superalloys