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Grain refinement and the stability of dendrites growing into undercooled pure metals and alloys

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2 Author(s)
Mullis, A.M. ; School of Materials, University of Leeds, Leeds LS2 9JT, United Kingdom ; Cochrane, R.F.

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We present an analysis of the stability of a dendrite against a small perturbation to the tip velocity. We find that dendritic growth in pure metals and alloys will become unstable above some upper critical undercooling ΔT2*. In alloys above a critical concentration, dendritic growth may also become unstable below a lower critical undercooling, ΔT1*. In the example systems studied, Ni–Cu and Ag–O, the location of these unstable regions shows remarkably close agreement with the onset of spontaneous grain refinement. We obtain values of ΔT2* for Ni and Ag of 195 K and 160 K, respectively, in good agreement with the observed values of 170 K and 133–153 K. © 1997 American Institute of Physics.

Published in:

Journal of Applied Physics  (Volume:82 ,  Issue: 8 )