PARAMETERS OF THE PERTURBED STATE OF THE DENDRITE TIP IN DEEPLY SUPERCOOLED NICKEL AND COPPER MELTS

Abstract

The object of study is the morphological stability of the tip of a free dendrite in a supercooled melt of a pure substance. Areas of deep supercooling are considered: for nickel DT > 166 K, for copper – DT > 180 K. A distinctive feature of the processes being studied is the presence of two propagation velocities of small disturbances (velocities of “sound”). The dependences of these rates on the supercooling of the melt were determined. The periodic and coordinate-aperiodic modes of perturbation of the growth line have been studied in detail. For these stable regimes, the possibility of observing the same speed of the disturbance wave in two processes, differing from each other in the size of the spatial inhomogeneity of the background in front of the wave and the characteristic wave attenuation times, was discovered. It is shown that aperiodic instability appears if, after the passage of the wave front, the width of the growth line inhomogeneity zone decreases. The resonant excitation mode of the dendrite tip demonstrates important differences between the properties of the nickel and copper melts. First of all, this relates to the temperature dependences of the resonant frequency and the speed of a standing wave formed in the vicinity of the vertex. Numerical calculations are presented and graphic information is presented illustrating the patterns of growth of nickel and copper dendrites.