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Multicomponent gamma-prime-strengthened Co-based superalloys with increased solvus temperature and decreased density

Published

Author(s)

Eric Lass, Daniel J. Sauza, David C. Dunand, David N. Seidman

Abstract

Several Co-Al-(W)-based -’ alloys are investigated in an attempt to combine recent results indicating significant increases in ’ solvus temperature with additions of Ni, Ta, and Ti, and reduced density with the substitution of Mo and Nb for W. A maximum solvus temperature of 1167±6 °C is achieved in an alloy with the composition (by mole fraction ×100) Co-30Ni-7Al-4Ti-7W-1Ta; while the composition Co-30Ni-7Al-4Ti-3Mo-2W-1Nb-1Ta (L19) exhibits a promising combination of high ’ volume fraction and solvus temperature, low density, and excellent two-phase -’microstructural stability. Atom probe tomographic measurement of L19 aged for 4 h at 900 °C indicates that Ni, Al, Ti, W, Nb, and Ta partition preferentially to the ’-precipitates while Co partitions strongly to the -matrix . Mo segregates to the /’ interface, resulting in a reduction in interfacial energy of -1.63±0.85 mJ·m-2. Decreasing the mole fraction of Ni from 30 % to 10 % results in decreased partitioning of Al and Ti to the γ’-phase and increases partitioning of Co, Mo, W, Nb, and Ta. From an analysis of coarsening behavior at 900 °C in Co-xNi-7Al-4Ti-3Mo-2W-1Nb-1Ta (x=10 and 30) interfacial energies of 19.3 mJ·m-2 and 10.0 mJ·m-2 are calculated for mole fractions of Ni of 10 % and 30 %, respectively. This decrease in interfacial energy with increasing Ni-content is potentially due to both Mo-segregation to the interface and a decrease in lattice misfit between the precipitate and matrix, and thus misfit strain energy.
Citation
ACTA Materialia
Volume
147

Keywords

Co-based, superalloy, microstructural evolution, alloy development
Created February 3, 2018, Updated February 6, 2018