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Crystals 2019, 9(3), 149; https://doi.org/10.3390/cryst9030149

On Crystal Mosaicity in Single Crystal Ni-Based Superalloys

1
Institute for Materials (IFM), Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
2
Interdisciplinary Centre for Advanced Materials Simulation (ICAMS), Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
*
Author to whom correspondence should be addressed.
Received: 22 February 2019 / Revised: 7 March 2019 / Accepted: 8 March 2019 / Published: 13 March 2019
(This article belongs to the Special Issue Fundamentals of Superalloys)
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Abstract

In the present work, we investigate the evolution of mosaicity during seeded Bridgman processing of technical Ni-based single crystal superalloys (SXs). For this purpose, we combine solidification experiments performed at different withdrawal rates between 45 and 720 mm/h with advanced optical microscopy and quantitative image analysis. The results obtained in the present work suggest that crystal mosaicity represents an inherent feature of SXs, which is related to elementary stochastic processes which govern dendritic solidification. In SXs, mosaicity is related to two factors: inherited mosaicity of the seed crystal and dendrite deformation. Individual SXs have unique mosaicity fingerprints. Most crystals differ in this respect, even when they were produced using identical processing conditions. Small differences in the orientation spread of the seed crystals and small stochastic orientation deviations continuously accumulate during dendritic solidification. Direct evidence for dendrite bending in a seeded Bridgman growth process is provided. It was observed that continuous or sudden bending affects the growth directions of dendrites. We provide evidence which shows that some dendrites continuously bend by 1.7° over a solidification distance of 25 mm. View Full-Text
Keywords: superalloys; crystal mosaicity; dendrite deformation; crystal growth; microstructure evolution superalloys; crystal mosaicity; dendrite deformation; crystal growth; microstructure evolution
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Hallensleben, P.; Scholz, F.; Thome, P.; Schaar, H.; Steinbach, I.; Eggeler, G.; Frenzel, J. On Crystal Mosaicity in Single Crystal Ni-Based Superalloys. Crystals 2019, 9, 149.

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