Morphological instabilities in rapid directional solidifications under local nonequilibrium conditions

We perform the linear morphological instability analysis in rapid direction al solidifications of dilute binary alloys considering the local nonequilib riums both in the bulk liquid and at the solid/liquid front. The generalize d Fick's law for mass transport in the melt and the velocity dependence of the segregation coefficient modified by Sobolev and coworkers are employed for the analysis. The result shows that, compared to the situation where no nequilibrium effects at the interface only are considered, the effect of th e local nonequilibrium in the bulk postpones the onset of the steady cellul ar instability but quickens the onset of the oscillatory cellular instabili ty. Consequently, smaller surface-energy and larger attachment kinetics are expected for the absolute-stability boundaries of the steady and oscillato ry cellular instabilities, respectively. (C) 1999 Published by Elsevier Sci ence B.V. All rights reserved.