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Influence of Process Parameter and Alloy Composition on Misoriented Eutectics in Single-Crystal Nickel-Based
Tobias Wittenzellner1, Shieren Sumarli2, Zijin Dai1
1Foundry Institute, RWTH Aachen University, 52072 Aachen, Germany.
Materials (Basel, Switzerland)
|June 28, 2023
Summary
Optimizing cooling rates and alloy composition in nickel-based superalloys prevents misoriented micro-structures. This research details how cooling affects nucleation and growth, crucial for defect-free single crystal casting.
Area of Science:
- Materials Science
- Metallurgy
- Crystallography
Background:
- Misoriented micro-structures in single crystals arise from complex interactions between process parameters and alloy composition.
- Understanding nucleation and growth mechanisms is vital for controlling solidification defects.
Purpose of the Study:
- To investigate the influence of cooling rates on the formation of misoriented micro-structures in carbon-free and carbon-containing nickel-based superalloys.
- To identify process parameters and alloy compositions that lead to solidification defects.
Main Methods:
- Utilized Bridgman and Bridgman-Stockbarger casting techniques under industrial and laboratory conditions.
- Analyzed six different alloy compositions, varying cooling rates, temperature gradients, and withdrawal rates.
Main Results:
- Eutectics exhibited random crystallographic orientation via homogeneous nucleation in the residual melt.
- In carbon-containing alloys, eutectics nucleated on carbides, especially at high carbon content and low cooling rates.
- Micro-stray grains formed from residual melt closure in carbides, leading to misoriented eutectics.
Conclusions:
- Identified critical process parameters (cooling rate, alloy composition) inducing misoriented micro-structures.
- Optimizing these parameters can prevent solidification defects in nickel-based superalloys.
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