The origin of freckles in unidirectionally solidified castings

Copley, S. M.; Giamei, A. F.; Johnson, Sylvia M.; Hornbecker, M. F.

doi:10.1007/bf02643435

Cited by 433 publications

(257 citation statements)

References 6 publications

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“…These fine equiaxed grains, or "freckles" have been studied in detail by Giamei and co-workers [2,3], and are associated with solute partitioning that progressively lowers the density of the liquid in the mushy zone, resulting in convective instabilities. Table II gives a comparison of the freckle composition to the average composition of interdendritic material (in areas of no freckling) for Alloy SX-1.…”

Section: Tvnes Of Grain Defectsmentioning

confidence: 99%

Grain Defect Formation During Directional Solidification of Nickel Base Single Crystals

Pollock¹,

Murphy²,

Goldman³

et al. 1992

Superalloys 1992 (Seventh International Symposium)

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Grain defect formation during solidification of nickel base single crystals has been studied in a series of alloys over a wide range of imposed thermal gradients and growth rates. Solute-driven convective instabilities, associated with high levels of Re and W and/or low levels of Ta, promote the formation of "freckle" defects as well as dendrite fragmentation and nucleation of misoriented grains. As the imposed positive thermal gradients at the solid-liquid interface decrease, grain nucleation events become more frequent until a general columnar to equiaxed transition is encountered. Transitions in solidification behavior and are shown to be consistent with changes in dendrite morphology and operative regimes of grain defect formation are characterized in terms of primary dendrite arm spacings.

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Section: Tvnes Of Grain Defectsmentioning

confidence: 99%

Grain Defect Formation During Directional Solidification of Nickel Base Single Crystals

Pollock¹,

Murphy²,

Goldman³

et al. 1992

Superalloys 1992 (Seventh International Symposium)

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“…A number of criteria for the prediction of A-segregates can be found in the literature, most relating to freckle formation in Ni-based alloys, and they are typically some function of the thermal gradient, G, and isotherm velocity, R: 15,207,208) . (7) where d, e and f are constants.…”

Section: The Suzuki and Rayleigh-number Criteriamentioning

confidence: 99%

“…Particularly noteworthy NH4Cl-H2O studies were carried out by McDonald and Hunt and Copley et al, and demonstrated that increased solidification times (and alloy freezing ranges) increased the severity of channel segregation. [13][14][15][16][17][18] The Pb-Sn system was also the subject of a considerable research effort. [19][20][21][22][23] Streat and Weinberg not only examined compositional and liquid- density effects in Pb-Sn, but also the extent of fluid drag within the mushy-zone network (i.e., the permeability, discussed below) on channel formation.…”

Section: )mentioning

confidence: 99%

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Pickering

2013

ISIJ Int.

143

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The macro-scale segregation of alloying elements during the casting continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still commonplace, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today's steel ingots are as chemically homogeneous as possible.This article briefly reviews the development of our current understanding of macrosegregation phenomena during the 20 th century, before going on to assess the latest developments in the field of macrosegregation modelling. The aim of the text is to highlight the shortcomings of applying contemporary macromodels to steel-ingot casting, and to suggest practical alternatives. In addition, the experimental characterisation of macrosegregation is explored, and a review of the various techniques currently available is presented.

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“…Transparent materials that freeze like metals have been used with some success: the Copley experiment gives an excellent example of the application to single crystal castings [29,30]. However, the influence of flow on fragmentation behaviour is difficult to assess owing to the conflicting requirements for clear imaging and imposable flow conditions [31,32].…”

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confidence: 99%

Dendrite Bending during Directional Solidification

Aveson¹,

Reinhart²,

Nguyen-Thi³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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In order to ascertain the origin of deformation and sub-grains in single crystal castings, an in situ, time-resolved X-ray radiographic imaging experiment was performed at the BM05 beam line of the European Synchrotron Radiation Facility (ESRF). This provided direct experimental evidence of the origin of crystallographic misorientation during the directional solidification of the nickel-based superalloy CMSX4. Solidification monitoring revealed that dendrites deform by bending and possibly torsion, and with deformation occurring early during dendrite growth, influencing the establishment of the dendritic array. These observations were related with electron backscattered diffraction data from ex situ samples. The bending and torsion contributions to deformation were extracted from the electron backscattered diffraction data using a data analysis scheme capable of isolating the deformation modes. In the component tested, bending was identified as the predominant deformation mode in sub-grain formation, but torsion effects were also seen to be significant.

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The origin of freckles in unidirectionally solidified castings

Cited by 433 publications

References 6 publications

Grain Defect Formation During Directional Solidification of Nickel Base Single Crystals

Grain Defect Formation During Directional Solidification of Nickel Base Single Crystals

Macrosegregation in Steel Ingots: The Applicability of Modelling and Characterisation Techniques

Dendrite Bending during Directional Solidification

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