Abstract
The coarsening kinetics and elemental partitioning behavior of γ’-(L12) precipitates in a γ(f.c.c.)-matrix for a model quaternary Co-8.8Al-8.9W-9.9Ni at.% superalloy are investigated utilizing isothermal aging conditions at 650, 800 and 900 °C. The γ′-precipitate mean radius, number density, and volume fraction, at 800 and 900 °C, were studied using scanning electron microscopy; the calculated temporal exponents associated with coarsening of γ′-precipitates display good agreement with model predictions for quasi-stationary coarsening. An atom probe tomographic (APT) investigation of the aged γ/γ′ microstructure at 650 °C demonstrates that the compositions and volume fractions of both phases vary continuously up to 4096 h. The aged microstructure at 650 °C consists of interconnected nanoscale γ′-precipitates, corroborated utilizing SEM for the 4096 h aged-specimen. The activation energy for coarsening is estimated for the temperature range 650–900 °C to be 283 kJ mol−1, in reasonable agreement with activation energies for diffusion of Al, W, and Ni in Co, suggesting that coarsening of γ′-precipitates is limited by bulk-diffusion. APT measurements of specimens aged for 1024 h at 800 and 900 °C demonstrate that the isothermal aging temperature has a significant effect on the compositions and partitioning behavior of Co, Al, W and Ni between the γ- and γ′-phases. The partitioning ratio of the concentrations between the γ′- and γ-phases is largest for W, decreasing linearly from 5.3 ± 0.1 at 650 °C to 2.1 ± 1.2 at 900 °C, and smallest for Co, decreasing from 0.86 ± 0.01 at 650 °C to 0.73 ± 0.01 at 900 °C.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 654-662 |
| Number of pages | 9 |
| Journal | Acta Materialia |
| Volume | 164 |
| DOIs | |
| State | Published - Feb 1 2019 |
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Keywords
- Atom-probe tomography (APT)
- Coarsening kinetics
- Cobalt-base superalloys
- Microstructure
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys
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γ’-(L12) precipitate evolution during isothermal aging of a Co–Al–W–Ni superalloy. / Sauza, Daniel J.; Dunand, David C; Noebe, Ronald D.; Seidman, David N.
In: Acta Materialia, Vol. 164, 01.02.2019, p. 654-662.Research output: Contribution to journal › Article
TY - JOUR
T1 - γ’-(L12) precipitate evolution during isothermal aging of a Co–Al–W–Ni superalloy
AU - Sauza, Daniel J.
AU - Dunand, David C
AU - Noebe, Ronald D.
AU - Seidman, David N
PY - 2019/2/1
Y1 - 2019/2/1
N2 - The coarsening kinetics and elemental partitioning behavior of γ’-(L12) precipitates in a γ(f.c.c.)-matrix for a model quaternary Co-8.8Al-8.9W-9.9Ni at.% superalloy are investigated utilizing isothermal aging conditions at 650, 800 and 900 °C. The γ′-precipitate mean radius, number density, and volume fraction, at 800 and 900 °C, were studied using scanning electron microscopy; the calculated temporal exponents associated with coarsening of γ′-precipitates display good agreement with model predictions for quasi-stationary coarsening. An atom probe tomographic (APT) investigation of the aged γ/γ′ microstructure at 650 °C demonstrates that the compositions and volume fractions of both phases vary continuously up to 4096 h. The aged microstructure at 650 °C consists of interconnected nanoscale γ′-precipitates, corroborated utilizing SEM for the 4096 h aged-specimen. The activation energy for coarsening is estimated for the temperature range 650–900 °C to be 283 kJ mol−1, in reasonable agreement with activation energies for diffusion of Al, W, and Ni in Co, suggesting that coarsening of γ′-precipitates is limited by bulk-diffusion. APT measurements of specimens aged for 1024 h at 800 and 900 °C demonstrate that the isothermal aging temperature has a significant effect on the compositions and partitioning behavior of Co, Al, W and Ni between the γ- and γ′-phases. The partitioning ratio of the concentrations between the γ′- and γ-phases is largest for W, decreasing linearly from 5.3 ± 0.1 at 650 °C to 2.1 ± 1.2 at 900 °C, and smallest for Co, decreasing from 0.86 ± 0.01 at 650 °C to 0.73 ± 0.01 at 900 °C.
AB - The coarsening kinetics and elemental partitioning behavior of γ’-(L12) precipitates in a γ(f.c.c.)-matrix for a model quaternary Co-8.8Al-8.9W-9.9Ni at.% superalloy are investigated utilizing isothermal aging conditions at 650, 800 and 900 °C. The γ′-precipitate mean radius, number density, and volume fraction, at 800 and 900 °C, were studied using scanning electron microscopy; the calculated temporal exponents associated with coarsening of γ′-precipitates display good agreement with model predictions for quasi-stationary coarsening. An atom probe tomographic (APT) investigation of the aged γ/γ′ microstructure at 650 °C demonstrates that the compositions and volume fractions of both phases vary continuously up to 4096 h. The aged microstructure at 650 °C consists of interconnected nanoscale γ′-precipitates, corroborated utilizing SEM for the 4096 h aged-specimen. The activation energy for coarsening is estimated for the temperature range 650–900 °C to be 283 kJ mol−1, in reasonable agreement with activation energies for diffusion of Al, W, and Ni in Co, suggesting that coarsening of γ′-precipitates is limited by bulk-diffusion. APT measurements of specimens aged for 1024 h at 800 and 900 °C demonstrate that the isothermal aging temperature has a significant effect on the compositions and partitioning behavior of Co, Al, W and Ni between the γ- and γ′-phases. The partitioning ratio of the concentrations between the γ′- and γ-phases is largest for W, decreasing linearly from 5.3 ± 0.1 at 650 °C to 2.1 ± 1.2 at 900 °C, and smallest for Co, decreasing from 0.86 ± 0.01 at 650 °C to 0.73 ± 0.01 at 900 °C.
KW - Atom-probe tomography (APT)
KW - Coarsening kinetics
KW - Cobalt-base superalloys
KW - Microstructure
UR - http://www.scopus.com/inward/record.url?scp=85056631822&partnerID=8YFLogxK
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U2 - 10.1016/j.actamat.2018.11.014
DO - 10.1016/j.actamat.2018.11.014
M3 - Article
VL - 164
SP - 654
EP - 662
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
ER -