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Morphological Stability of Electron Beam Melted Aluminum Alloys

Published online by Cambridge University Press:  15 February 2011

R. J. Schaefer ,
S. R. Coriell ,
R. Mehrabian ,
C. Fenimore  and
F. S. Biancaniello
R. J. Schaefer
Affiliation:
National Bureau of Standards, Washington, D.C. 20234
S. R. Coriell
Affiliation:
National Bureau of Standards, Washington, D.C. 20234
R. Mehrabian
Affiliation:
National Bureau of Standards, Washington, D.C. 20234
C. Fenimore
Affiliation:
National Bureau of Standards, Washington, D.C. 20234
F. S. Biancaniello
Affiliation:
National Bureau of Standards, Washington, D.C. 20234
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Abstract

For constant velocity solidification, morphological stability theory delineates the temperature gradients required for plane front solidification of a specific alloy. Using electron beams, surface heating of metals can be carried out with sufficiently well characterized thermal input to permit reliable use of computer models of melting and solidification. From numerical calculations, the growth velocity and temperature gradients as a function of position during resolidification can be obtained; combining these results with (constant velocity) morphological stability theory indicates the resolidification regimes for which the plane front is unstable. Presumably, completely planar solidification may be attained by selecting heating modes such that the region of instability is totally avoided, but the expected interface morphology is more difficult to predict if the interface passes briefly through an unstable region and then re-enters a region of stability. Aluminum-silver and aluminum-manganese alloys were melted under an electron beam with particular emphasis on attaining solidification sufficiently rapidly to satisfy the gradient-independent absolute stability condition. It was found that the velocities required to produce stability were considerably larger than expected.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 8 , 1981 , 79
Copyright
Copyright © Materials Research Society 1982

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References

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