Metallurgical and Materials Transactions A

, Volume 43, Issue 3, pp 965–976 | Cite as

Structure Refinement by a Liquid Metal Cooling Solidification Process for Single-Crystal Nickel-Base Superalloys

  • C. L. Brundidge
  • D. van Drasek
  • B. Wang
  • T. M. Pollock
Article
First Online:

Abstract

Single crystals of a nickel-base superalloy were directionally solidified (DS) over a range of cooling rates to evaluate the benefits of a new high thermal gradient solidification process. Solidification experiments were conducted on cylindrical bars with a liquid-metal-enhanced cooling process. This higher gradient casting process was evaluated for the degree of structure refinement, microstructural variability, and porosity distributions. Cylindrical bars of 1.6-cm diameter were solidified at rates between 8.4 and 21.2 mm/min using a tin-based, liquid metal cooling (LMC) technique and at a rate of 3.4 mm/min with a conventional Bridgman process. The LMC process produced a refined microstructure with average primary dendrite arm spacing (PDAS) and secondary dendrite arm spacing (SDAS) values as low as 164 and 25 μm, respectively, for the bar geometry evaluated. An optimum intermediate withdrawal velocity of 12.7 mm/min produced up to a 50 and 60 pct refinement in PDAS and SDAS, respectively. Further increases in withdrawal velocity produced smaller SDAS and pore sizes, but undesirable grain boundaries and excessive secondary dendrite arm growth. Voronoi tessellation methods were used to examine the extremes of the dendrite arm spacings in comparison to the average measurements, the packing of dendrites, and the correlation of porosity size and location with the dendrite structure. A simple expression for prediction of the maximum pore size is developed.

Keywords

Mushy Zone Primary Dendrite Withdrawal Rate Voronoi Cell Directionally Solidify 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Notes

Acknowledgments

The authors acknowledge the assistance of C.J. Torbet. The funding provided by General Electric Aviation (GE-USA Program) is also gratefully acknowledged.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2011

Authors and Affiliations

  • C. L. Brundidge
    • 1
  • D. van Drasek
    • 1
  • B. Wang
    • 1
  • T. M. Pollock
    • 1
    • 2
  1. 1.Department of Materials Science and EngineeringUniversity of MichiganAnn ArborUSA
  2. 2.Materials DepartmentUniversity of CaliforniaSanta BarbaraUSA

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