Morphological instabilities in rapid directioanl solidifications under lcola nonequilibrium condtions under local nonequilibrium conditions

摘要

We perform the linear morphological instability analysis in rapid directioahl solidificaitons of dilue binary alloys considering the local nonequilibrums both in the bulk liquid and a the solid/liquid front. The generalized Fick's law for mass transport in the melt and the velocity dependence of he segregation coefficient modified by Sobolev and coworkers are employed for hte analysis. Thue result shows that, comapred to the situaiton where nonequilibrium effects at the interace only are considered, the effect of the locla nonequilibrium in the bulk postpones the onset of the steady cellular instability but quickens the onset of the oscillatory cellular instabiity. Consequently, smaller surface-energy and larger atachmenbt kinetics are expected for the absolute-stability boundaries of the steady and oscillatory cellulr insabilities, respectively.