Effects of solid-solid boundary anisotropy on directional solidification microstructures

Abstract : The microstructures arising from the solidification processing possess various types of boundaries: solid(S)-liquid(L) interfaces, grain boundaries (GB), interphase boundaries (IB). Whereas solid-liquid interface has been investigated extensively, relatively little attention has been paid to the S-S boundaries (GB and IB). Recently, it has been found that S-S boundary anisotropy can also have a significant influence, particularly on the overall orientation selection of the growing patterns. The present thesis investigates the effects of GB and IB anisotropy through simulations of solidification morphologies. We use a recent multi-phase field model for this study. In essence, we work with a grand-canonical functional combining the interfacial and bulk free energies of the system and then minimising it with respect to the field variables to obtain the equations of motion for the phase fields and the composition fields. We use this code to study three problems stemming from the directional solidification of lamellar eutectics and polycrystals with a particular focus on the effects of the solid-solid boundary anisotropy. During thin-film directional solidification experiments on lamellar eutectics, it has been observed that in response to the IB anisotropy, lamellae grow at an angle with the growth axis. We characterize this drift angle using our numerical simulations and then compare it successfully with a recent theoretical prediction. Then, we exploit this IB anisotropy in bulk lamellar eutectics to understand the emergence of certain minimum energy directions in the system leading to preferred orientations in the microstructure. Then, we repeat our thin-film eutectic study for polycrystals with grain boundaries, motivated by the fact that anisotropic low-angle grain boundaries or sub-boundaries grow at an angle with respect to the growth axis. We quantify this tilt angle and compare it successfully with a recent analytical prediction. In this way, we establish the influence of the solid-solid boundary anisotropy on the directionally solidified microstructures.
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Submitted on : Thursday, September 24, 2015 - 3:04:34 PM
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  • HAL Id : tel-01204752, version 1

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Supriyo Ghosh. Effects of solid-solid boundary anisotropy on directional solidification microstructures. Engineering Sciences [physics]. Ecole Polytechnqiue, 2015. English. ⟨tel-01204752⟩

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