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Influence of Gravity Driven Convection on the Directional Solidification of Bi/MnBi Eutectic Composites

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Abstract

The role of gravity on Bridgman-Stockbarger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA soundinq rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Ri/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnRi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed, normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50%, for the low gravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97% of the theoretical maximum. Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnRi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

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Acknowledgements

This research was partially supported by the Materials Processinq in Space Program of the National Aeronautics and Space Administration under contract NAS8-32219. The authors wishe to thank P. Adler of Grumman, M. Glicksman of Rensselaer Polytechnic Institute, W. Wilcox of Clarkson College, S. Coriell of NBS and L. Testardi of NASA for technical advice. Special thanks to the Grumman staff of W. Poit for sample preparation, J. Drauch for metallographic preparation and R. Lange for magnetic property characterization. The authors also thank the staff of the Francis Bitter National Magnet Laboratory for their assistance.

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Authors and Affiliations

  1. Metals Science Laboratory, Research and Development Center, Grumman Aerospace Corporation, Bethpaqe, New York, USA

    Ron G. Pirich & D. J. Larson

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  1. Ron G. Pirich
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  2. D. J. Larson
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Pirich, R.G., Larson, D.J. Influence of Gravity Driven Convection on the Directional Solidification of Bi/MnBi Eutectic Composites. MRS Online Proceedings Library 9, 523–531 (1981). https://doi.org/10.1557/PROC-9-523

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