Experimental measurements of sidebranching in thermal dendrites under terrestrial-gravity and microgravity conditions

Abstract

We perform sidebranch measurements on pure succinonitrile dendrites grown in both microgravity and terrestrial-gravity conditions for a set of supercoolings within the range 0.1-1.0 K. Two distinct types of sidebranch regions, uniform and coarsening, exist, and are characterized by the distance from the tip at which the region began, D(i), and the average spacing of sidebranches within that region, lambda(i). There does not appear to be any significant dependence on either gravity level or supercooling when D(i) or lambda(i) are normalized with respect to the radius of curvature of the tip, R. The apparently constant normalized proportionality factor between D(i), lambda(i), and R, regardless of the relative importance of diffusion and convective heat transport, demonstrates self-similarity between dendrites of different length scales propagating under various heat transfer conditions. However, when the form of the sidebranch envelope is defined by a power law relating the amplitude and relative positions of the sidebranches normalized to the radius of the tip, the form is seen to have significant variations with supercooling between the terrestrial gravity and microgravity growth dendrites. Furthermore, both the amplitude coefficient and exponent from the power-law regressions of the microgravity data are statistically different (95% confidence level) than their terrestrial counterparts.

Spontaneous deterministic side-branching behavior in phase-field simulations of equiaxed dendritic growth

“…Imaging of dendritic growth in transparent analogue casting systems, such as succinonitrile [1] and xenon [2], show that close to the tip region the dendrite is apparently free from sidebranching. Moving away from the tip small oscillations are initiated which grow as they move down the dendrite trunk.…”

An adaptive, fully implicit multigrid phase-field model for the quantitative simulation of non-isothermal binary alloy solidification

“…The analytical solution for such a crystal growing into its undercooled melt is degenerate in that it relates the Peclet number, and not the growth velocity, to undercooling, where the Peclet number is defined as α ρ 2 = V Pt (1) with α the thermal diffusivity in the melt. Consequently, at a given undercooling an infinite set of solutions are admissable, subject to the condition Vρ = constant.…”

Materials solidification physics in space

“…Important theoretical milestones are in this respect the discovery of the Mullins-Sekerka instability, marginal stability and microscopic solvability theories providing a basic understanding of dendrite formation. A critical test of these theories was performed with microgravity experiments by Glicksman and coworkers in which established flow-free conditions of heat transfer [4][5][6] allowed a careful validation of theoretical models. The same approach is presently under development for modelling of solidification processes with microstructural features.…”