Dendrite sidebranches in directional solidification

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2022-05
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Lyons, Trevor Daniel
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Naplitano, Ralph E
Chumbley, Scott
Kramer, Matt J
Lee, Jonghyun
Evans, Jim W
Trivedi, Rohit K
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Materials Science and Engineering
Abstract
Through an evolution of gradient at constant velocity limit cycle growth mechanisms have been found in dendrites grown by directional solidification. Image analysis of experimental observations confirms these limit cycles are formed between the radius and the first instability that develops into a sidebranch. Experiments at all gradients are characterized based on the natural period of sidebranching. The natural period is constant with gradient until it increases with the transition to limit cycle growth, and in this constant region is comparable to the characteristic solute diffusion time. Limit cycle growth periods are described by the characteristic interaction time between the tip and forming instability. At high gradients the period is found with components of the characteristic interaction timescale and instability size found by the marginal stability selection criteria. Novel experiments in dynamic velocities are introduced in which the natural period of sidebranching is controlled by the application of a square waveform of velocity.
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