A freckle criterion for the solidification of superalloys with a tilted solidification front

Yang, Wulin; deBarbadillo, J.J.; Morita, Koki; Suzuki, Toshio; Chen, Wei; Chang, Keh‐Minn

doi:10.1007/s11837-004-0202-7

Cited by 22 publications

(32 citation statements)

References 11 publications

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“…Several studies have shown that lower cooling rates during DS result in a high propensity for the freckle formation and coarsely distributed c/c¢ eutectic pools. [1,[8][9][10][11] In particular, the latter is known to have a detrimental effect on high-temperature creep resistance. For example, Yan et al [12] reported that the eutectic region, specifically the interface between c/c¢ eutectic and matrix, is the most preferential crack initiation site during creep rupture.…”

Section: Introductionmentioning

confidence: 99%

A Comparative Study of the γ/γ′ Eutectic Evolution During the Solidification of Ni-Base Superalloys

Seo

Lee

Yoo

et al. 2011

Metall Mater Trans A

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The evolution of c/c¢ eutectic during the solidification of Ni-base superalloys CMSX-10 and CMSX-4 was investigated over a wide range of cooling rates. The microsegregation behavior during solidification was also quantitatively examined to clarify the influence of elemental segregation on the evolution of c/c¢ eutectic. In the cooling rate ranges investigated (0.9 to 138.4 K/min (0.9 to 138.4°C/min)), the c/c¢ eutectic fraction in CMSX-10 was found to be more than 2 times higher than that in CMSX-4 at a given cooling rate. However, the dependence of the c/c¢ eutectic fraction on the cooling rate in both alloys showed a similar tendency; i.e., the c/c¢ eutectic fraction increased with increasing the cooling rate and then exhibited a maximum plateau at and above the certain critical cooling rate in both alloys. This critical cooling rate was found to be dependent on the alloy composition and was estimated to be about 12 K/min (12°C/min) and 25 K/min (25°C/min) for CMSX-10 and CMSX-4, respectively. The calculated solid compositions based on the modified Scheil model revealed that even a small compositional difference of total c¢ forming elements in the initial composition of the alloy can play a significant role in the as-cast eutectic fraction during the solidification of Ni-base superalloys. The evolution of the c/c¢ eutectic fraction with respect to the cooling rate could be rationalized by taking into account the effects of back-diffusion in solid and dendrite arm coarsening on decreasing the extent of microsegregation.

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Section: Introductionmentioning

confidence: 99%

A Comparative Study of the γ/γ′ Eutectic Evolution During the Solidification of Ni-Base Superalloys

Seo

Lee

Yoo

et al. 2011

Metall Mater Trans A

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“…[25,26] Results showed that freckles can propagate without the influence of the electromagnetic Lorentz force, indicating that it would be possible that freckles in VAR ingots have a nucleation mechanism that does not necessarily depend on the bulk liquid convection.…”

Section: Density Inversionmentioning

confidence: 99%

“…In a subsequent work, Yang et al extended their form to include the effect of the slope of the solidification front and performed horizontal solidification experiments for verification. [25] The modified criterion form was weak in that the formulation included the angle that the velocity vector formed with the isotherms, which is not known a priori, and makes it difficult to establish an accurate prediction of freckling.…”

Section: Density Inversionmentioning

confidence: 99%

On the Formulation of a Freckling Criterion for Ni-Based Superalloy Vacuum Arc Remelting Ingots

Valdés

King

Liu

2010

Metall Mater Trans A

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A criterion for freckling prediction that includes the effect of a tilted solidification front was proposed and evaluated with experimental data available in the literature. The criterion is based on the maximum local Rayleigh number in the mush layer and was developed using Flemings' criterion and assuming that the interdendritic liquid flow is governed by the Darcy law. The proposed form preserves the anisotropic nature of the permeability tensor throughout the derivation and provides improved resolution on freckle prediction. A clear separation between the freckled and nonfreckled experiments was obtained for all compositions. The effect of the tilted solidification front over the freckling potential was corroborated, and the results suggested that the directionality of permeability affects the location within the mush layer of the potential nucleation sites for the channels leading to freckles. A threshold zone was determined from the enclosing experiments data, and the range contained one of the proposed critical values for superalloys, which previously was developed by a completely different method.

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“…verification. 23 The modified form had the weakness that it included the angle that the velocity vector formed with the isotherms, which is not known before hand, and makes it difficult to establish an accurate prediction of freckling. Auburtin et al 25 and 0.95.…”

Section: Prediction Of Freckles Formationmentioning

confidence: 99%

Solidification Front Tilt Angle Effect on Potential Nucleation Sites for Freckling in the Remelt of Ni-Base Superalloys

Valdés¹,

Cowen²,

Jablonski³

et al. 2010

7th International Symposium on Superalloy 718 and Derivatives (2010)

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By considering the mushy layer as a porous media with variable permeability, a Rayleigh number based freckling criterion was developed from the Flemings ratio between the magnitude of the interdendritic flow velocity and the solidification rate. The proposed form includes the effect of the tilt angle by preserving the anisotropic nature of the permeability tensor throughout the derivation and uses Poirier's experimentally determined functional forms for the parallel and perpendicular components. The proposed form of Rayleigh number criterion was found to provide better resolution when evaluated against available experimental data in the literature.Especially, it showed that the nucleation of channels in the mushy layer leading to freckles is equally probable in the proximity of the tips of the dendrites or deeper in the mushy layer, for example at approximately 0.7 liquid fraction and 0.4 liquid fraction respectively, depending on the angle of tilt of the solidification front.

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A freckle criterion for the solidification of superalloys with a tilted solidification front

Cited by 22 publications

References 11 publications

A Comparative Study of the γ/γ′ Eutectic Evolution During the Solidification of Ni-Base Superalloys

A Comparative Study of the γ/γ′ Eutectic Evolution During the Solidification of Ni-Base Superalloys

On the Formulation of a Freckling Criterion for Ni-Based Superalloy Vacuum Arc Remelting Ingots

Solidification Front Tilt Angle Effect on Potential Nucleation Sites for Freckling in the Remelt of Ni-Base Superalloys

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