Abstract
Polycrystalline Co-10Ni-(9 – x)Al-(9 – x)W-2xTi at% (x = 0, 1, 2, 3, 4) alloys with γ(f.c.c.) plus γ′(L12) microstructures are investigated, where the γ′(L12)-formers Al and W are replaced with Ti. Upon aging, the initially cuboidal γ′(L12)-precipitates grow and develop a rounded morphology. After 256 h of aging at 1000 °C, the precipitates in the 6 and 8 at% Ti alloys coalesce and develop an irregular, elongated morphology. After 1000 h of aging, replacement of W and Al with Ti increases both the mean radius, <R>, and volume fraction, ϕ, of the γ′(L12)-phase from <R> = 463 nm and ϕ = 8% for 2 at% Ti to <R> = 722 nm and ϕ = 52% for 8 at% Ti. Composition measurements of the γ(f.c.c.)-matrix and γ′(L12)-precipitates demonstrate that Ti substitutes for W and Al in the γ′(L12)-precipitates, increases the partitioning of W to γ′(L12), and changes the partitioning behavior of Al from a mild γ′(L12)-former to a mild γ(f.c.c.)-former. The grain boundaries in the aged alloys exhibit W-rich precipitates, most likely μ(Co7W6)-type, which do not destabilize the γ(f.c.c.) plus γ′(L12) microstructure within the grains. Four important benefits accrue from replacing W and Al with Ti: (i) the alloys’ mass density decrease; (ii) the γ′(L12)-solvus temperature increases; (iii) the γ′(L12) volume fraction formed during aging at 1273 K (1000 °C) increases; and (iv) the 0.2% offset flow stress increases.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 122-132 |
| Number of pages | 11 |
| Journal | Materials Science and Engineering A |
| Volume | 705 |
| DOIs | |
| State | Published - Sep 29 2017 |
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Keywords
- Cobalt superalloy
- Flow stress
- Gamma prime
- High-temperature stability
- Precipitation strengthening
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
Cite this
}
Effects of titanium substitutions for aluminum and tungsten in Co-10Ni-9Al-9W (at%) superalloys. / Bocchini, Peter J.; Sudbrack, Chantal K.; Noebe, Ronald D.; Dunand, David C; Seidman, David N.
In: Materials Science and Engineering A, Vol. 705, 29.09.2017, p. 122-132.Research output: Contribution to journal › Article
TY - JOUR
T1 - Effects of titanium substitutions for aluminum and tungsten in Co-10Ni-9Al-9W (at%) superalloys
AU - Bocchini, Peter J.
AU - Sudbrack, Chantal K.
AU - Noebe, Ronald D.
AU - Dunand, David C
AU - Seidman, David N
PY - 2017/9/29
Y1 - 2017/9/29
N2 - Polycrystalline Co-10Ni-(9 – x)Al-(9 – x)W-2xTi at% (x = 0, 1, 2, 3, 4) alloys with γ(f.c.c.) plus γ′(L12) microstructures are investigated, where the γ′(L12)-formers Al and W are replaced with Ti. Upon aging, the initially cuboidal γ′(L12)-precipitates grow and develop a rounded morphology. After 256 h of aging at 1000 °C, the precipitates in the 6 and 8 at% Ti alloys coalesce and develop an irregular, elongated morphology. After 1000 h of aging, replacement of W and Al with Ti increases both the mean radius, <R>, and volume fraction, ϕ, of the γ′(L12)-phase from <R> = 463 nm and ϕ = 8% for 2 at% Ti to <R> = 722 nm and ϕ = 52% for 8 at% Ti. Composition measurements of the γ(f.c.c.)-matrix and γ′(L12)-precipitates demonstrate that Ti substitutes for W and Al in the γ′(L12)-precipitates, increases the partitioning of W to γ′(L12), and changes the partitioning behavior of Al from a mild γ′(L12)-former to a mild γ(f.c.c.)-former. The grain boundaries in the aged alloys exhibit W-rich precipitates, most likely μ(Co7W6)-type, which do not destabilize the γ(f.c.c.) plus γ′(L12) microstructure within the grains. Four important benefits accrue from replacing W and Al with Ti: (i) the alloys’ mass density decrease; (ii) the γ′(L12)-solvus temperature increases; (iii) the γ′(L12) volume fraction formed during aging at 1273 K (1000 °C) increases; and (iv) the 0.2% offset flow stress increases.
AB - Polycrystalline Co-10Ni-(9 – x)Al-(9 – x)W-2xTi at% (x = 0, 1, 2, 3, 4) alloys with γ(f.c.c.) plus γ′(L12) microstructures are investigated, where the γ′(L12)-formers Al and W are replaced with Ti. Upon aging, the initially cuboidal γ′(L12)-precipitates grow and develop a rounded morphology. After 256 h of aging at 1000 °C, the precipitates in the 6 and 8 at% Ti alloys coalesce and develop an irregular, elongated morphology. After 1000 h of aging, replacement of W and Al with Ti increases both the mean radius, <R>, and volume fraction, ϕ, of the γ′(L12)-phase from <R> = 463 nm and ϕ = 8% for 2 at% Ti to <R> = 722 nm and ϕ = 52% for 8 at% Ti. Composition measurements of the γ(f.c.c.)-matrix and γ′(L12)-precipitates demonstrate that Ti substitutes for W and Al in the γ′(L12)-precipitates, increases the partitioning of W to γ′(L12), and changes the partitioning behavior of Al from a mild γ′(L12)-former to a mild γ(f.c.c.)-former. The grain boundaries in the aged alloys exhibit W-rich precipitates, most likely μ(Co7W6)-type, which do not destabilize the γ(f.c.c.) plus γ′(L12) microstructure within the grains. Four important benefits accrue from replacing W and Al with Ti: (i) the alloys’ mass density decrease; (ii) the γ′(L12)-solvus temperature increases; (iii) the γ′(L12) volume fraction formed during aging at 1273 K (1000 °C) increases; and (iv) the 0.2% offset flow stress increases.
KW - Cobalt superalloy
KW - Flow stress
KW - Gamma prime
KW - High-temperature stability
KW - Precipitation strengthening
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UR - http://www.scopus.com/inward/citedby.url?scp=85027960475&partnerID=8YFLogxK
U2 - 10.1016/j.msea.2017.08.034
DO - 10.1016/j.msea.2017.08.034
M3 - Article
VL - 705
SP - 122
EP - 132
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 -