SPATIAL-TEMPORAL INHOMOGENEITIES AT THE PHASE BOUNDARY OF HIGH-SPEED
 CRYSTALLIZATION OF A UNDERCOOLED MELT

Abstract

The object of study is the growth line of a free dendrite in a undercooled melt of a pure substance. The perturbed
 state of the growth line at a finite distance from the top of the dendrite has been studied. It is in this part
 of the crystallization front that the appearance of side branches is observed. Two main variants are considered:
 aperiodic and coordinate-periodic background, along which the perturbation wave propagates. An important role
 of the characteristic size of the zone of spatial inhomogeneity of the background is revealed, and quantitative estimates
 of the threshold values of this size are given. The dependences of the wave velocity on the angle of sharpening
 of the growth line and on the width of the inhomogeneity zone are studied. Examples are given demonstrating
 that the direction of wave movement (from the top to the periphery or from the periphery to the top) affects the morphological
 stability/instability of the growth line. The properties of the perturbation damping parameter are studied
 in detail. Numerical modeling of the properties of the growth process was performed for nickel and copper melts
 at undercoolings equal to 160 K and 180 K respectively. The result of the calculations is the correlation "wave
 speed – taper angle – size of the inhomogeneity zone", "attenuation parameter – taper angle". The presented graphical
 information demonstrates quantitative differences in the growth properties of nickel and copper dendrites.