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Surface Segregation during Directional Solidification of Ni-Base Superalloys

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Abstract

Some aspects pertaining to the increased microsegregation at the external casting surface during directional solidification of a typical Ni-base superalloy, CMSX 10N, are presented. Increased eutectic coverage was observed at the external surface along the solidification length. This eutectic appears as a thin segregated layer proud of the secondary dendrite arms preventing them from impinging onto the mold wall. The extent of surface eutectic coverage was represented as a fractional measure of the ingot perimeter. Possible mechanisms focusing on the following: (1) interaction between mold and metal, (2) inclination of primary dendrite, and (3) contraction of the dendrite network have been investigated in relation to the observed phenomenon. We deduce that the most likely explanation is associated with the contraction of the dendritic network, which qualitatively accounts both for the observed morphology and the increased eutectic fraction at the external surface of the casting.

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Acknowledgments

The authors acknowledge the contribution of Dr. Mahmoud Ardakani, Department of Materials, Imperial College (London), who assisted with the SEM. One of the authors (HBD) acknowledges the Royal Society and EPSRC for offering a Royal Society Industry Fellowship and Rolls-Royce plc for hosting him at the Precision Casting Facility (PCF), Derby.

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Authors and Affiliations

  1. Department of Materials Science, University of Cambridge, Cambridge, CB2 3QZ, United Kingdom

    G. Brewster (EngD Student)

  2. Operations and Engineering and Technology, Rolls-Royce plc, Derby, DE24 8BJ, United Kingdom

    G. Brewster (EngD Student)

  3. Precision Casting Facility, Rolls-Royce plc, Derby, UK

    H.B. Dong (Royal Society Industry Fellow) & N. D’Souza (Casting Specialist)

  4. Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom

    N.R. Green (Professor)

Authors
  1. G. Brewster
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  2. H.B. Dong
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  3. N.R. Green
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  4. N. D’Souza
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Corresponding author

Correspondence to N. D’Souza.

Additional information

Manuscript submitted August 18, 2007.

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Brewster, G., Dong, H., Green, N. et al. Surface Segregation during Directional Solidification of Ni-Base Superalloys. Metall Mater Trans B 39, 87–93 (2008). https://doi.org/10.1007/s11663-007-9118-2

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  • DOI: https://doi.org/10.1007/s11663-007-9118-2

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