Microstructural evolution and high-temperature strength of a γ(f.c.c.)/γ’(L12) Co–Al–W–Ti–B superalloy

Daniel J. Sauza, David C Dunand*, David N Seidman

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

We characterized the microstructural features and mechanical performance of a model Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) alloy consisting of γ(L12)-precipitates in a γ(f.c.c.)-matrix. Scanning electron microscopy (SEM) was used to follow the isothermal aging of the microstructure at 900 and 1000 °C for 256 h, and 950 °C for 1000 h. The compositions of the γ'(L12)-precipitates and γ(f.c.c.)-matrix were evaluated by atom-probe tomography (APT) for solution-treated and air-cooled conditions, as well as in specimens aged at 950 °C for 16 and 100 h. Boron was shown to partition preferentially to the γ'(L12)-precipitates, and profiles taken across the γ(f.c.c.)-matrix channels in both aged specimens revealed confined segregation of Al at one of the two γ(f.c.c.)/γ′(L12) heterophase interfaces. After aging at 950 °C for 16 h, Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) exhibited anomalous flow-strength behavior in the range 625–900 °C with a peak yield stress of 822 MPa between 800 and 825 °C. Compressive creep tests performed at 850 °C demonstrated a creep strength comparable to archival literature results for Co–9Al–9W-0.12B (at.%), despite a smaller γ′(L12)-volume fraction and lack of strengthening borides along the grain boundaries (GBs). The activation energy for creep in the temperature range 800–900 °C was 606 kJ mol−1. The post-creep microstructure consists of rafted γ′(L12)-precipitates perpendicular to the compression axis, consistent with the positive γ(f.c.c.)/γ'(L12) lattice parameter misfit character of this class of alloys. Creep failure could occur due to GB embrittlement caused by deleterious Ti-rich (L21 or B2) and D019 phases formed at the GBs during creep.

Original languageEnglish (US)
Pages (from-to)427-438
Number of pages12
JournalActa Materialia
Volume174
DOIs
StatePublished - Aug 1 2019

Fingerprint

Microstructural evolution
Superalloys
Creep
Precipitates
Grain boundaries
Temperature
Boron Compounds
Aging of materials
Microstructure
Boron
Borides
Embrittlement
Lattice constants
Tomography
Yield stress
Volume fraction
Activation energy
Atoms
Scanning electron microscopy
Air

Keywords

  • Atom probe tomography (APT)
  • Cobalt-base superalloys
  • Creep
  • Mechanical properties
  • Microstructure

ASJC Scopus subject areas

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

Cite this

@article{c5922f3c5edb4f81991955452d527d41,
title = "Microstructural evolution and high-temperature strength of a γ(f.c.c.)/γ’(L12) Co–Al–W–Ti–B superalloy",
abstract = "We characterized the microstructural features and mechanical performance of a model Co-5.6Al-5.8W-6.6Ti-0.12B (at.{\%}) alloy consisting of γ(L12)-precipitates in a γ(f.c.c.)-matrix. Scanning electron microscopy (SEM) was used to follow the isothermal aging of the microstructure at 900 and 1000 °C for 256 h, and 950 °C for 1000 h. The compositions of the γ'(L12)-precipitates and γ(f.c.c.)-matrix were evaluated by atom-probe tomography (APT) for solution-treated and air-cooled conditions, as well as in specimens aged at 950 °C for 16 and 100 h. Boron was shown to partition preferentially to the γ'(L12)-precipitates, and profiles taken across the γ(f.c.c.)-matrix channels in both aged specimens revealed confined segregation of Al at one of the two γ(f.c.c.)/γ′(L12) heterophase interfaces. After aging at 950 °C for 16 h, Co-5.6Al-5.8W-6.6Ti-0.12B (at.{\%}) exhibited anomalous flow-strength behavior in the range 625–900 °C with a peak yield stress of 822 MPa between 800 and 825 °C. Compressive creep tests performed at 850 °C demonstrated a creep strength comparable to archival literature results for Co–9Al–9W-0.12B (at.{\%}), despite a smaller γ′(L12)-volume fraction and lack of strengthening borides along the grain boundaries (GBs). The activation energy for creep in the temperature range 800–900 °C was 606 kJ mol−1. The post-creep microstructure consists of rafted γ′(L12)-precipitates perpendicular to the compression axis, consistent with the positive γ(f.c.c.)/γ'(L12) lattice parameter misfit character of this class of alloys. Creep failure could occur due to GB embrittlement caused by deleterious Ti-rich (L21 or B2) and D019 phases formed at the GBs during creep.",
keywords = "Atom probe tomography (APT), Cobalt-base superalloys, Creep, Mechanical properties, Microstructure",
author = "Sauza, {Daniel J.} and Dunand, {David C} and Seidman, {David N}",
year = "2019",
month = "8",
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Microstructural evolution and high-temperature strength of a γ(f.c.c.)/γ’(L12) Co–Al–W–Ti–B superalloy. / Sauza, Daniel J.; Dunand, David C; Seidman, David N.

In: Acta Materialia, Vol. 174, 01.08.2019, p. 427-438.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Microstructural evolution and high-temperature strength of a γ(f.c.c.)/γ’(L12) Co–Al–W–Ti–B superalloy

AU - Sauza, Daniel J.

AU - Dunand, David C

AU - Seidman, David N

PY - 2019/8/1

Y1 - 2019/8/1

N2 - We characterized the microstructural features and mechanical performance of a model Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) alloy consisting of γ(L12)-precipitates in a γ(f.c.c.)-matrix. Scanning electron microscopy (SEM) was used to follow the isothermal aging of the microstructure at 900 and 1000 °C for 256 h, and 950 °C for 1000 h. The compositions of the γ'(L12)-precipitates and γ(f.c.c.)-matrix were evaluated by atom-probe tomography (APT) for solution-treated and air-cooled conditions, as well as in specimens aged at 950 °C for 16 and 100 h. Boron was shown to partition preferentially to the γ'(L12)-precipitates, and profiles taken across the γ(f.c.c.)-matrix channels in both aged specimens revealed confined segregation of Al at one of the two γ(f.c.c.)/γ′(L12) heterophase interfaces. After aging at 950 °C for 16 h, Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) exhibited anomalous flow-strength behavior in the range 625–900 °C with a peak yield stress of 822 MPa between 800 and 825 °C. Compressive creep tests performed at 850 °C demonstrated a creep strength comparable to archival literature results for Co–9Al–9W-0.12B (at.%), despite a smaller γ′(L12)-volume fraction and lack of strengthening borides along the grain boundaries (GBs). The activation energy for creep in the temperature range 800–900 °C was 606 kJ mol−1. The post-creep microstructure consists of rafted γ′(L12)-precipitates perpendicular to the compression axis, consistent with the positive γ(f.c.c.)/γ'(L12) lattice parameter misfit character of this class of alloys. Creep failure could occur due to GB embrittlement caused by deleterious Ti-rich (L21 or B2) and D019 phases formed at the GBs during creep.

AB - We characterized the microstructural features and mechanical performance of a model Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) alloy consisting of γ(L12)-precipitates in a γ(f.c.c.)-matrix. Scanning electron microscopy (SEM) was used to follow the isothermal aging of the microstructure at 900 and 1000 °C for 256 h, and 950 °C for 1000 h. The compositions of the γ'(L12)-precipitates and γ(f.c.c.)-matrix were evaluated by atom-probe tomography (APT) for solution-treated and air-cooled conditions, as well as in specimens aged at 950 °C for 16 and 100 h. Boron was shown to partition preferentially to the γ'(L12)-precipitates, and profiles taken across the γ(f.c.c.)-matrix channels in both aged specimens revealed confined segregation of Al at one of the two γ(f.c.c.)/γ′(L12) heterophase interfaces. After aging at 950 °C for 16 h, Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) exhibited anomalous flow-strength behavior in the range 625–900 °C with a peak yield stress of 822 MPa between 800 and 825 °C. Compressive creep tests performed at 850 °C demonstrated a creep strength comparable to archival literature results for Co–9Al–9W-0.12B (at.%), despite a smaller γ′(L12)-volume fraction and lack of strengthening borides along the grain boundaries (GBs). The activation energy for creep in the temperature range 800–900 °C was 606 kJ mol−1. The post-creep microstructure consists of rafted γ′(L12)-precipitates perpendicular to the compression axis, consistent with the positive γ(f.c.c.)/γ'(L12) lattice parameter misfit character of this class of alloys. Creep failure could occur due to GB embrittlement caused by deleterious Ti-rich (L21 or B2) and D019 phases formed at the GBs during creep.

KW - Atom probe tomography (APT)

KW - Cobalt-base superalloys

KW - Creep

KW - Mechanical properties

KW - Microstructure

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U2 - 10.1016/j.actamat.2019.05.058

DO - 10.1016/j.actamat.2019.05.058

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EP - 438

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

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