The influence of molybdenum on the γ/’phase in experimental nickel-base superalloys

The microstructural stability of nickel-based superalloys is critical for maintaining alloy performance during service in gas turbine engines. In this study, the precipitate evolution in a model polycrystalline Ni-based superalloy during aging to 1000 hours has been studied via transmission electron microscopy, atom probe tomography, and neutron diffraction. Variations in phase composition and precipitate morphology, size, and volume fraction were observed during aging, while the constrained lattice misfit remained constant at approximately zero. The experimental composition of the γ matrix phase was consistent with thermodynamic equilibrium predictions, while significant differences were identified between the experimental and predicted results from the γ′ phase. These results have implications for the evolution of mechanical properties in service and their prediction using modeling methods.

Section: B Precipitate Compositionsupporting

confidence: 90%

Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy

Goodfellow

Galindo-Nava

Christofidou

et al. 2017

“…[6] often much lower, with reported values of ␦ all less than It is noted that the preceding alloys, and their heat treat-0.34 pct in the alloys considered here. [42][43][44][45] A more detailed ment, provide cases that are widely different. The composidiscussion of the results for binary alloys and the effect of tion and solvus temperatures of the alloys are quite different coherency strains will be made later in this article.…”

Section: Estimation Of Critical Parametersmentioning

confidence: 99%

The coarsening kinetics of γ′ particles in nickel-based alloys

Li¹,

Saunders²,

Miodownik³

2002

116

The present article describes a method for calculating the coarsening rate of ␥ Ј in Ni-based superalloys, which has been applied to both binary Ni-Al alloys and a wide range of multicomponent alloys. A standard coarsening equation is utilized, but innovative methods for calculating the critical input parameters are presented. The article details methods of estimating interfacial energies and the effective diffusion coefficients that are key parameters for the coarsening model. Self-consistent calculations are made via a computer program in which the only input required is the composition of the alloys and the temperature of coarsening. The effects of coherent strain on the coarsening process have also been analyzed and discussed.

“…Other studies also show that in dilute ␥ ϩ ␥' alloys, ␦ can be positive; [11,12] however, it is typically negative in highly alloyed commercial superalloys. The value of ␦ increases among the alloys in the following order: Co and Mo, base, W, Ti, Nb, and Ta.…”

Section: B Phase Lattice Parametersmentioning

confidence: 99%

The effects of composition and γ′/γ lattice parameter mismatch on the critical resolved shear stresses for octahedral and cube slip in NiAlCrX alloys

Miner

1997

Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the ␥' phase, and about 3 at. pct of X in the ␥ '. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 ЊC, which is about the peak strength temperature. The CRSS oct and CRSS cube are discussed in relation to those of Ni 3 (Al, X) ␥' alloys taken from the literature and the ␥'/␥ lattice mismatch. The CRSS oct of the ␥ ϩ ␥ ' alloys reflected a similar compositional dependence to that of both the CRSS oct of the ␥' phase and the ␥ '/␥ lattice parameter mismatch. The CRSS cube of the ␥ ϩ ␥' alloys also reflected the compositional dependence of the ␥ '/␥ mismatch, but bore no similarity to that of CRSS cube for ␥' alloys since it is controlled by the ␥ matrix. The ratio of CRSS cube /CRSS oct was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSS cube /CRSS oct was related to the degree in which elements partition to the ␥' rather than the ␥ phase.