Temporal evolution of a model Co-Al-W superalloy aged at 650 °C and 750 °C

Peter J. Bocchini*, Chantal K. Sudbrack, Ronald D. Noebe, David N Seidman

*Corresponding author for this work

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The temporal evolution of a γ(f.c.c.)/γ’ (L12) Co-8.8Al-7.3 W superalloy aged at 650 °C (10 min–4096 h) and 750 °C (10 min–256 h) is studied utilizing atom-probe tomography (APT), scanning electron microscopy, and Vickers microhardness testing. The evolution of the phase compositions, γ’ (L12) volume fraction, and mean precipitate radius, <R2-D(t)> are determined. Coarsening rate constants and temporal exponents are calculated for <R-D(t)> of the γ’ (L12)-nanoprecipitates. The temporal exponents are found to be generally close to 1/p = 1/3 as required for diffusion-limited coarsening. Tungsten solid-solubility is significantly reduced in the γ(f.c.c.)-matrix at 650 °C (0.54 ± 0.04 at. %) and 750 °C (1.35 ± 0.06 at. %) when compared with aging at 900 °C (5.5 at. %). The value of <R2D(t)> of the γ’ (L12)-nanoprecipitates increases with increasing aging time corresponding to an increase in the Vickers microhardness; the peak strength was not, however, achieved for the aging times investigated. The morphology of the γ’ (L12)-nanoprecipitates begins as spheroids but transitions to cuboids at longer aging times, with final the γ’ (L12) volume fractions for aging at 650 °C and 750 °C being ϕ = 53% and 54%, respectively. The effect of quench-rate (either furnace-cooled, air-cooled, oil quenched, or water quenched) from a supersolvus temperature of 1050 °C on the microstructure of the alloy is also investigated. Slow cooling (furnace and air-cooling) is shown to result in a uniform distribution of nanometer sized γ’ (L12)-nanoprecipitates, unlike Ni-based superalloys in which the γ’ (L12)-nanoprecipitates form in a non-uniform or multimodal distribution.

Original languageEnglish (US)
Pages (from-to)197-208
Number of pages12
JournalActa Materialia
Volume159
DOIs
StatePublished - Oct 15 2018

Fingerprint

Superalloys
Aging of materials
Coarsening
Microhardness
Volume fraction
Furnaces
Cooling
Tungsten
Air
Phase composition
Tomography
Precipitates
Rate constants
Oils
Solubility
Atoms
Microstructure
Scanning electron microscopy
Water
Testing

Keywords

  • Atom-probe tomography
  • Co-Al-W
  • Cobalt
  • Gamma prime
  • Superalloy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

Cite this

Bocchini, Peter J. ; Sudbrack, Chantal K. ; Noebe, Ronald D. ; Seidman, David N. / Temporal evolution of a model Co-Al-W superalloy aged at 650 °C and 750 °C. In: Acta Materialia. 2018 ; Vol. 159. pp. 197-208.
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Temporal evolution of a model Co-Al-W superalloy aged at 650 °C and 750 °C. / Bocchini, Peter J.; Sudbrack, Chantal K.; Noebe, Ronald D.; Seidman, David N.

In: Acta Materialia, Vol. 159, 15.10.2018, p. 197-208.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Temporal evolution of a model Co-Al-W superalloy aged at 650 °C and 750 °C

AU - Bocchini, Peter J.

AU - Sudbrack, Chantal K.

AU - Noebe, Ronald D.

AU - Seidman, David N

PY - 2018/10/15

Y1 - 2018/10/15

N2 - The temporal evolution of a γ(f.c.c.)/γ’ (L12) Co-8.8Al-7.3 W superalloy aged at 650 °C (10 min–4096 h) and 750 °C (10 min–256 h) is studied utilizing atom-probe tomography (APT), scanning electron microscopy, and Vickers microhardness testing. The evolution of the phase compositions, γ’ (L12) volume fraction, and mean precipitate radius, <R2-D(t)> are determined. Coarsening rate constants and temporal exponents are calculated for <R-D(t)> of the γ’ (L12)-nanoprecipitates. The temporal exponents are found to be generally close to 1/p = 1/3 as required for diffusion-limited coarsening. Tungsten solid-solubility is significantly reduced in the γ(f.c.c.)-matrix at 650 °C (0.54 ± 0.04 at. %) and 750 °C (1.35 ± 0.06 at. %) when compared with aging at 900 °C (5.5 at. %). The value of <R2D(t)> of the γ’ (L12)-nanoprecipitates increases with increasing aging time corresponding to an increase in the Vickers microhardness; the peak strength was not, however, achieved for the aging times investigated. The morphology of the γ’ (L12)-nanoprecipitates begins as spheroids but transitions to cuboids at longer aging times, with final the γ’ (L12) volume fractions for aging at 650 °C and 750 °C being ϕ = 53% and 54%, respectively. The effect of quench-rate (either furnace-cooled, air-cooled, oil quenched, or water quenched) from a supersolvus temperature of 1050 °C on the microstructure of the alloy is also investigated. Slow cooling (furnace and air-cooling) is shown to result in a uniform distribution of nanometer sized γ’ (L12)-nanoprecipitates, unlike Ni-based superalloys in which the γ’ (L12)-nanoprecipitates form in a non-uniform or multimodal distribution.

AB - The temporal evolution of a γ(f.c.c.)/γ’ (L12) Co-8.8Al-7.3 W superalloy aged at 650 °C (10 min–4096 h) and 750 °C (10 min–256 h) is studied utilizing atom-probe tomography (APT), scanning electron microscopy, and Vickers microhardness testing. The evolution of the phase compositions, γ’ (L12) volume fraction, and mean precipitate radius, <R2-D(t)> are determined. Coarsening rate constants and temporal exponents are calculated for <R-D(t)> of the γ’ (L12)-nanoprecipitates. The temporal exponents are found to be generally close to 1/p = 1/3 as required for diffusion-limited coarsening. Tungsten solid-solubility is significantly reduced in the γ(f.c.c.)-matrix at 650 °C (0.54 ± 0.04 at. %) and 750 °C (1.35 ± 0.06 at. %) when compared with aging at 900 °C (5.5 at. %). The value of <R2D(t)> of the γ’ (L12)-nanoprecipitates increases with increasing aging time corresponding to an increase in the Vickers microhardness; the peak strength was not, however, achieved for the aging times investigated. The morphology of the γ’ (L12)-nanoprecipitates begins as spheroids but transitions to cuboids at longer aging times, with final the γ’ (L12) volume fractions for aging at 650 °C and 750 °C being ϕ = 53% and 54%, respectively. The effect of quench-rate (either furnace-cooled, air-cooled, oil quenched, or water quenched) from a supersolvus temperature of 1050 °C on the microstructure of the alloy is also investigated. Slow cooling (furnace and air-cooling) is shown to result in a uniform distribution of nanometer sized γ’ (L12)-nanoprecipitates, unlike Ni-based superalloys in which the γ’ (L12)-nanoprecipitates form in a non-uniform or multimodal distribution.

KW - Atom-probe tomography

KW - Co-Al-W

KW - Cobalt

KW - Gamma prime

KW - Superalloy

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