Prediction of the densities of liquid Ni-based superalloys

Mukai, Kusuhiro; Li, Zushu; Mills, Kenneth C.

doi:10.1007/s11663-005-0027-y

Cited by 31 publications

(35 citation statements)

References 9 publications

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“…The calculated molar volumes are in good agreement sessile drop experiments, for elemental Ni at these temperatures the error is 1.6% and 0.8% for 1750 K and 1830 K, respectively [2]. Fig.…”

Section: Local Orderingsupporting

confidence: 77%

Molecular-Dynamics Simulations of Molten Ni-based Superalloys

Woodward¹,

Lill²,

Asta³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Fundamental parameters of liquid metal alloys are calculated using a first principles approach, based on Density Functional Theory (DFT), with the goal of informing models of defect formation during solidification processing. Ab-initio molecular dynamic simulations (AIMD) are applied to liquid metal alloys ranging from simple metals to Rene-N4 and CMSX-4 to predict molar volumes (density), diffusion rates and local ordering. These include elemental Ni, Ni-5.4X, Ni-20X, and Ni-10Al-2.8X (X= W, Re, and Ta) (at%) alloys at 1750 and 1830 K. Calculated kinetics and the atomic distribution in the liquids indicate that simulations of 500 atoms run for approximately 7 ps converge the time-averaged properties, including molar volume. Overall diffusion rates and molar volumes are in good agreement with available experimental measurements, though the AIMD predictions appear to systematically underestimate thermal expansion. The method is then used to predict density inversion in three additional alloys, Ni-14Al-3W, CMSX-4 and Rene-N4 for temperatures and compositions expected in the mushy zone during directional solidification. Density inversion is predicted for these three alloys based on density and density contrast in the mushy zone, the prediction and ranking of the effect is consistent with previous studies. Predictions for molar volume are compared with the recent parameterization of molar volumes using extensive measurements of binary alloys. AIMD calculations validate the underlying assumptions of these models and illustrate the bounds in alloy chemistry for applying such techniques. IntroductionWith the increasing complexity in alloy chemistry and airfoil geometry over succeeding generations of turbine engines the probability of forming processing defects (freckles) during directional solidification has increased. These calculations offer a new approach for determining the fundamental parameters required for modeling aspects of this processing path. Convective instabilities responsible for freckle defects are produced by variations in liquid-metal density with composition and temperature across the solidification zone. A systems design leading to optimal material and component performance requires a quantitative model for predicting processing regimes for defect free castings over the widest range of refractory metal compositions. Models of thermo-chemical convection in the mushy zone have shown that such instabilities occur when a Rayleigh number exceeds a critical value [1]. The Rayleigh number, R, is a measure of the ratio of the buoyancy force to the retarding frictional force:

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Section: Local Orderingsupporting

confidence: 77%

Molecular-Dynamics Simulations of Molten Ni-based Superalloys

Woodward¹,

Lill²,

Asta³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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“…In Table I, values from the most recent parameterization of molten superalloy densities, due to Mukai et al, [8] are listed along side the AIMD results. For elemental Ni, and the binary Ni-Al and Ni-W systems, the Mukai model reproduces well the directly measured densities obtained at these same compositions and temperatures.…”

Section: Results and Analysismentioning

confidence: 99%

“…Recently, Mukai et al [6][7][8] performed extensive measurements of the densities of several binary liquid Ni-based alloys, and a few representative ternaries, as functions of c and T . The results of their measurements have been used to develop a thorough parameterization for V (c, T ) in superalloys.…”

Section: Introductionmentioning

confidence: 99%

“…The results of their measurements have been used to develop a thorough parameterization for V (c, T ) in superalloys. [8] Due to the lack of sufficient data for multicomponent systems, a key assumption made in the development of the parameterization is that the partial-molar volume of each solute is independent of the compositions of the other species. The effects upon V (c, T ) arising from the interactions between solute atoms of different types are thus neglected.…”

Section: Introductionmentioning

confidence: 99%

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Ab-Initio Molecular Dynamics Simulations of Molten Ni-Based Superalloys (Preprint)

Woodward¹,

Lill²

2011

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information , 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YY)2. REPORT TYPE 3. DATES COVERED (From -To) ABSTRACTIn casting of single-crystal turbine blades for jet engines, the formation of solidification defects has become an increasingly important problem due to the rising levels of refractory elements in Ni-based superalloys. Refractory elements, which are beneficial for high-temperature mechanical properties, enhance density-driven convective instabilities underlying the formation of freckle defects in directional solidification. In support of an effort aimed at the development of validated mathematical criteria for predicting solidification-defect formation in superalloys, ab-initio molecular dynamics simulations have been performed to calculate volumes of Ni-AI, Ni-W, Ni-Re, Ni-Ta, Ni-Al-Re, NiAl-Ta, Ni-Al-W, and complex chemistries approximating RENE-N4 melts. Introduction : In casting of single-crystal turbine blades for jet engines, the formation of solidification defects has become an increasingly important problem due to the rising levels of refractory elements in Ni-based superalloys. Refractory elements, which are beneficial for high-temperature mechanical properties, enhance density-driven convective instabilities underlying the formation of freckle defects in directional solidification. In support of an effort aimed at the development of validated mathematical criteria for predicting solidification-defect formation in superalloys, ab-initio molecular dynamics simulations have been performed to calculate volumes of Ni-Al, Ni-W, Ni-Re, Ni-Ta, Ni-Al-Re, Ni-Al-Ta, Ni-Al-W and complex chemistries approximating RENE-N4 melts. SUBJECT TERMSObjective : Derive physical quantities related to the formation of highly mis-oriented grains during the solidification of single-crystal Ni-based superalloys. During directional solidification, the mass-density difference between the hot liquid near the solid-liquid interface and the cooler melt at the top and side-walls of the casting, is the driving force for convection and associated formation of solidification defects. This mass-density difference originates from both the composition and temperature d...

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“…Values for viscosity (µ) and density (!) of the molten fluid during simulation have been approximated from calculations and predictions in the literature [21,22].…”

Section: Methodsmentioning

confidence: 99%

Characterization of Three-Dimensional Dendritic Structures in Nickel-Base Single Crystals for Investigation of Defect Formation

Madison¹,

Spowart²,

Rowenhorst³

et al. 2008

Superalloys 2008 (Eleventh International Symposium)

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During solidification, solute-induced convective instabilities at the solid -liquid interface can result in the formation of defects such as freckles and misoriented grains in superalloy single crystals. These defects can be particularly detrimental to the properties of single crystal nickel-base superalloys. Unfortunately, detailed understanding of fluid flow at the scale of the dendritic structure has yet to be fully understood, particularly under conditions in which heat extraction is non-axial. The objective of this research is to develop a technique for quantifying the dendritic structure and morphology at the solid -liquid interface for the purpose of providing direct input into computational fluid flow modeling. Using the RoboMET.3D serial sectioning system, threedimensional datasets of dendritic structure at the solidification front have been obtained for René N4 abruptly decanted during solidification. Distribution and arrangement of solid and liquid in the vicinity of dendrite tips is analyzed and the implications for defect formation are discussed.

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Prediction of the densities of liquid Ni-based superalloys

Cited by 31 publications

References 9 publications

Molecular-Dynamics Simulations of Molten Ni-based Superalloys

Molecular-Dynamics Simulations of Molten Ni-based Superalloys

Ab-Initio Molecular Dynamics Simulations of Molten Ni-Based Superalloys (Preprint)

Characterization of Three-Dimensional Dendritic Structures in Nickel-Base Single Crystals for Investigation of Defect Formation

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