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Comparison of Structures of Gas Atomized and of Emulsified Highly Undercooled Ni-Sn Alloy Droplets

Published online by Cambridge University Press:  25 February 2011

Michiharu Yamamoto ,
Yanzhong Wu ,
Yuh Shiohara  and
Merton C. Flemings
Michiharu Yamamoto
Affiliation:
Dept. of Materials Science and Engineering, MIT, Cambridge, MA 02139 now Nippon Mining Co., Ltd., Tokyo, JAPAN
Yanzhong Wu
Affiliation:
Dept. of Materials Science and Engineering, MIT, Cambridge, MA 02139
Yuh Shiohara
Affiliation:
Materials Processing Center, MIT, Cambridge, MA 02139
Merton C. Flemings
Affiliation:
Dept. of Materials Science and Engineering, MIT, Cambridge, MA 02139
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Abstract

A comparison is made of microstructures of droplets of Ni-Sn alloys rapidly solidified (a) by gas atomization and (b) in a glass emulsifying medium. Cooling rate of the gas atomized particles ranged from 103 to 106K/s depending on droplet diameter (20-230μm). In the hypoeutectic alloy studied (Ni-25wt%Sn), most particles showed a dendritic structure. These same particles, melted and resolidified in a glass medium using DTA (Differential Thermal Analysis), showed undercoolings up to 280K: the structures were dendritic at low undercoolings and non-dendritic at undercoolings above about 220K. It is concluded that (1) the gas atomized particles exhibited little or no undercooling before nucleation, (2) the solidification time of the undercooled emulsified droplets is substantially less than that of gas atomized droplets, and (3) the undercooling required to achieve non-dendritic structure depends on sample size.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 58 , 1985 , 411
Copyright
Copyright © Materials Research Society 1986

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References

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