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.
N1 - Funding Information:
This research was supported by the US Department of Energy, Office of Basic Energy Sciences (Dr. John Vetrano, grant monitor) through grant DE-FG02-98ER45721. P.J.B. received partial support from the NASA Aeronautics Scholarship Program and Fixed Wing project. This work made use of the Materials Characterization and Imaging Facility and the Central Laboratory for Materials Mechanical Properties (CLaMMP), which receives support from the MRSEC Program (DMR-112162) at Northwestern University. This research also made use of the Electron Probe Instrumentation Center (EPIC) facility of the Northwestern University Atomic and Nanoscale Characterization Experimental Center (NUANCE), which receives support from the Materials Research Science and Engineering Center (MRSEC) program (NSF DMR-1121262); the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN. The authors also thank Messrs. Jesse Bierer and Grant Feichter (NASA Glenn Research Center, Cleveland, OH) for their assistance with arc-melting and heat-treating the specimens and Dr. Daniel Sauza for his assistance with sample preparation.
Funding Information:
This research was supported by the US Department of Energy , Office of Basic Energy Sciences (Dr. John Vetrano, grant monitor) through grant DE-FG02-98ER45721 . P.J.B. received partial support from the NASA Aeronautics Scholarship Program and Fixed Wing project. This work made use of the Materials Characterization and Imaging Facility and the Central Laboratory for Materials Mechanical Properties (CLaMMP), which receives support from the MRSEC Program ( DMR-112162 ) at Northwestern University. This research also made use of the Electron Probe Instrumentation Center (EPIC) facility of the Northwestern University Atomic and Nanoscale Characterization Experimental Center (NUANCE), which receives support from the Materials Research Science and Engineering Center ( MRSEC ) program (NSF DMR-1121262 ); the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN. The authors also thank Messrs. Jesse Bierer and Grant Feichter (NASA Glenn Research Center, Cleveland, OH) for their assistance with arc-melting and heat-treating the specimens and Dr. Daniel Sauza for his assistance with sample preparation.
Publisher Copyright:
© 2017 Elsevier B.V.
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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U2 - 10.1016/j.msea.2017.08.034
DO - 10.1016/j.msea.2017.08.034
M3 - Article
AN - SCOPUS:85027960475
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 -