Phase field assisted analysis of a solidification based metal refinement process

A. Viardin, B. Böttger, M. Apel
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引用次数: 4

Abstract

Ultra pure metals have various applications, e. g. as electrical conductors. Crystallization from the melt, e. g. via zone melting, using the segregation of impurities at the solidification front is the basic mechanism behind different technical processes for the refining of metals and semi-metals. In this paper, we focus on a crystallization methodology with a gas cooled tube (“cooled finger”) dipped into a metallic melt in a rotating crucible. The necessary requirement for purification in a solidification process is a morphologically stable solidification front. This is the only way to enable macroscopic separation of the impurities, e. g. by convection. For cellular or dendritic solidification morphologies, the segregated impurities are trapped into the interdendritic melt and remain as microsegregations in the solidified metal. Morphological stability depends on the temperature gradient G at the solidification front, the solidification front velocity V front and thermodynamic alloy properties like the segregation coefficients of the impurity elements. To quantify the impact of these parameters on the morphological evolution, especially on the planar/cellular transition and thus on microsegregation profiles, phase field simulations coupled to a thermodynamic database are performed for an aluminium melt with three impurities, Si, Mn and Fe. In particular, we have investigated the morphology evolution from the start of solidification at the cooled finger towards a stationary growth regime, because in the technical process a significant fraction of the melt solidifies along the initial transient. To solve the transient long range temperature evolution on an experimental length scale, the temperature field has been calculated using the homoenthalpic approach together with a 1D temperature field approximation. The simulations provide the process window for an energy efficient purification process, i. e. low thermal gradients, and elucidate the benefit of melt convection.

基于凝固的金属细化过程相场辅助分析
超纯金属有多种用途,例如作为导电体。熔体的结晶,例如通过区域熔化,在凝固前沿利用杂质的偏析是金属和半金属精炼不同技术过程背后的基本机制。在本文中,我们重点研究了一种结晶方法,将气体冷却管(“冷却手指”)浸入旋转坩埚中的金属熔体中。在凝固过程中进行净化的必要条件是具有形态稳定的凝固前沿。这是实现杂质宏观分离的唯一方法,例如通过对流。对于细胞或枝晶凝固形态,分离的杂质被困在枝晶间熔体中,并以微偏析的形式留在凝固的金属中。形态稳定性取决于凝固前沿温度梯度G、凝固前沿速度V和杂质元素偏析系数等合金热力学性能。为了量化这些参数对形态演变的影响,特别是对平面/胞状转变的影响,从而对微偏析曲线的影响,对含有三种杂质(Si, Mn和Fe)的铝熔体进行了相场模拟和热力学数据库的耦合。特别是,我们研究了从冷却手指凝固开始到固定生长状态的形态演变,因为在技术过程中,很大一部分熔体沿着初始瞬态凝固。为了在实验长度尺度上求解瞬态长范围温度演化,采用同焓法结合一维温度场近似计算了温度场。模拟提供了一个高效的净化过程的过程窗口,即低热梯度,并阐明了熔体对流的好处。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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期刊介绍: Journal of Materials Science: Materials Theory publishes all areas of theoretical materials science and related computational methods. The scope covers mechanical, physical and chemical problems in metals and alloys, ceramics, polymers, functional and biological materials at all scales and addresses the structure, synthesis and properties of materials. Proposing novel theoretical concepts, models, and/or mathematical and computational formalisms to advance state-of-the-art technology is critical for submission to the Journal of Materials Science: Materials Theory. The journal highly encourages contributions focusing on data-driven research, materials informatics, and the integration of theory and data analysis as new ways to predict, design, and conceptualize materials behavior.
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