Microstructural and creep properties of boron- and zirconium-containing cobalt-based superalloys

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

*Corresponding author for this work

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline γ(f.c.c.) plus γ'(L12) strengthened Co-9.5Al-7.5W-X at% alloys (X=0-Ternary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at%) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions display no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57±1.04 atoms nm−2 was found for B at a GB in the 0.01B alloy and 2.88±0.81 and 2.40±0.84 atoms nm−2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

Original languageEnglish (US)
Pages (from-to)260-269
Number of pages10
JournalMaterials Science and Engineering A
Volume682
DOIs
StatePublished - Jan 13 2017

Fingerprint

creep properties
Boron
heat resistant alloys
Cobalt
Superalloys
Zirconium
Creep
boron
cobalt
Grain boundaries
grain boundaries
creep strength
Precipitates
precipitates
cohesion
Atoms
Boron Compounds
atoms
creep tests
Creep resistance

Keywords

  • Atom-probe tomography (APT)
  • Cobalt-base superalloys
  • Creep
  • Gamma prime
  • Grain boundaries

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

@article{00f5d0aa795e4a988cadc7818938d4b1,
title = "Microstructural and creep properties of boron- and zirconium-containing cobalt-based superalloys",
abstract = "The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline γ(f.c.c.) plus γ'(L12) strengthened Co-9.5Al-7.5W-X at{\%} alloys (X=0-Ternary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at{\%}) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions display no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57±1.04 atoms nm−2 was found for B at a GB in the 0.01B alloy and 2.88±0.81 and 2.40±0.84 atoms nm−2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6{\%}, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.",
keywords = "Atom-probe tomography (APT), Cobalt-base superalloys, Creep, Gamma prime, Grain boundaries",
author = "Bocchini, {Peter J.} and Sudbrack, {Chantal K.} and Noebe, {Ronald D.} and Dunand, {David C} and Seidman, {David N}",
year = "2017",
month = "1",
day = "13",
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language = "English (US)",
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Microstructural and creep properties of boron- and zirconium-containing cobalt-based superalloys. / Bocchini, Peter J.; Sudbrack, Chantal K.; Noebe, Ronald D.; Dunand, David C; Seidman, David N.

In: Materials Science and Engineering A, Vol. 682, 13.01.2017, p. 260-269.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Microstructural and creep properties of boron- and zirconium-containing cobalt-based superalloys

AU - Bocchini, Peter J.

AU - Sudbrack, Chantal K.

AU - Noebe, Ronald D.

AU - Dunand, David C

AU - Seidman, David N

PY - 2017/1/13

Y1 - 2017/1/13

N2 - The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline γ(f.c.c.) plus γ'(L12) strengthened Co-9.5Al-7.5W-X at% alloys (X=0-Ternary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at%) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions display no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57±1.04 atoms nm−2 was found for B at a GB in the 0.01B alloy and 2.88±0.81 and 2.40±0.84 atoms nm−2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

AB - The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength in polycrystalline γ(f.c.c.) plus γ'(L12) strengthened Co-9.5Al-7.5W-X at% alloys (X=0-Ternary, 0.05B, 0.01B, 0.05Zr, and 0.005B-0.05Zr at%) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion, compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions display no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57±1.04 atoms nm−2 was found for B at a GB in the 0.01B alloy and 2.88±0.81 and 2.40±0.84 atoms nm−2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in the other four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributed to the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease in the minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

KW - Atom-probe tomography (APT)

KW - Cobalt-base superalloys

KW - Creep

KW - Gamma prime

KW - Grain boundaries

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U2 - 10.1016/j.msea.2016.10.124

DO - 10.1016/j.msea.2016.10.124

M3 - Article

VL - 682

SP - 260

EP - 269

JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing

JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing

SN - 0921-5093

ER -