共查询到19条相似文献,搜索用时 109 毫秒
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凝固过程中自然对流作用下组织演化模拟 总被引:5,自引:2,他引:5
以Fe-C二元合金铸锭为例,模拟了其冷却过程中自然对流对凝固组织形成的影响。首先采用有限差分方法计算宏观温度场、速度场和溶质场。然后将计算得到的温度场和溶质场作为已知值耦合元胞自动机方法(CA)对铸锭的组织演化进行模拟。通过模拟发现,在冷却过程中自然对流改变了铸锭内的温度场、速度场和溶质场的分布,进而影响到凝固组织的形貌。 相似文献
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通过实验观察Al-Si合金的凝固组织,测量枝晶组织的二次枝晶臂间距,并分析温度对凝固组织的影响。在相场模型中引入重力引起的自然对流以预测实验条件下Al-Si合金凝固组织的演变。模拟结果与实验结果吻合良好,验证了本文中提出的模拟方法的可靠性。基于本文的耦合模型,开展一系列不同溶质含量合金柱状晶和等轴晶组织生长的二维和三维模拟,发现合金中溶质含量对凝固组织的演变几乎没有影响,而溶质膨胀系数对枝晶尖端移动速度有显著影响。本文中采用的算法极大地加快计算效率,因此,大规模的数值模拟使难以直接通过同步辐射实验观察的Al-Si合金凝固组织演变过程的研究成为可能。 相似文献
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相场模型及其在凝固组织模拟中的研究进展 总被引:2,自引:0,他引:2
相场法作为一种模拟凝固微观组织的有效方法,是目前研究的热点.对相场模型的基本原理、数值计算方法以及在凝固组织模拟中的研究进展进行了综述,提出了相场模型在微观组织模拟中存在的主要问题以及今后的发展方向. 相似文献
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垂直定向凝固条件下通道偏析形成过程的数值模拟 总被引:4,自引:0,他引:4
建立了描述合金凝固过程热-溶质对流和宏观偏析形成过程的数学模型。模型中耦合求解了凝固过程中质量、动量、能量和溶质守恒方程;同时,基于固液两相区中温度和成分的耦合关系建立了固相分数场的更新方法。利用该模型模拟了底部冷却的二维矩形区域内Fe-C合金凝固过程中通道偏析的形成和发展过程。模拟结果表明,垂直定向凝固条件下通道偏析形成于液相线前沿附近,而不是两相区内部。这一结果很好地支持了文献中基于实验观察提出的通道偏析形成机理。 相似文献
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I. Steinbach 《Acta Materialia》2009,57(9):2640-2645
Competing self-organization between the solidification pattern and the convection pattern in a directional solidification environment is investigated theoretically and by phase-field simulations. Melt flow introduces a mode of transport with broken symmetry dependent on the direction of growth relative to the vector of gravity. A stable and an unstable regime can be distinguished. The interaction between spacing selection and convection leads to a new type of scaling that explains results from phase-field simulations and solidification experiments under enhanced gravity. 相似文献
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Yun ChenAbdoul-Aziz Bogno Na Min XiaoBernard Billia Xiu Hong KangHenri Nguyen-Thi Xing Hong LuoDian Zhong Li 《Acta Materialia》2012,60(1):199-207
The initial transient during directional solidification of an Al-4 wt.% Cu alloy was simulated by a quantitative phase-field model solved with the adaptive finite element method. The simulated solidification process was compared with the related analytical theory and in situ and real time observations by means of X-ray radiography at the European Synchrotron Radiation Facility. The simulated velocity of the planar interface and solute profile ahead of the solidification front in the liquid are close to the predictions of the Warren-Langer model of the initial planar solidification transient, but in fair quantitative agreement with experimental results only at early stages of planar solidification. After the accelerated flat interface lost its stability a transition to cellular solidification was initiated. The initial cell spacing predicted by the phase-field simulation agreed well with the experimental observations in the region where the cell growth direction was perpendicular to the fluid flow, whereas a discrepancy was obvious in the corners where the fluid flow was parallel to growth. An analytical relation describing the wavelength of the initial solid-liquid interface corrugations under diffusion-limited transport is screened out by comparing the phase-field simulation data with expressions based upon the Mullins-Sekerka linear stability analysis theory or derived for primary spacing. The gravity-driven natural convection in the experiment resulted in misfits between the phase-field predictions and the experimental observations in the late stage of planar solidification, onset and development of morphological instability. 相似文献
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Using phase-field theory we demonstrate that osmotic stress may result in intense convection in solidifying eutectic systems. Under isothermal conditions the natural convection is of osmotic origin, and driven by the non-equilibrium composition field. Osmotic forces arise mostly in the interface layer, since large concentration gradients are localized near the triple junctions of the phases. Tuning friction forces at the solid-liquid interface controls the intensity of fluid flow. We have found that convection in the low friction regime significantly affects microstructural pattern formation. Osmotic convection-driven instability of the solid-liquid interface is observed that leads to cellular and dendritic eutectic crystal growth. The mechanism we propose is distinct from diffusive instability that is widely acknowledged as the main cause of cellular and fingerlike patterns. 相似文献
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《Acta Materialia》1999,47(13):3663-3678
Two-dimensional Ostwald ripening of an Al–4% Cu alloy solid/liquid mush in the presence of melt convection, and the influence of ripening on the flow, is studied numerically using a recent extension of the phase-field method that accounts for flow in the liquid phase. Through a parametric study, the ripening kinetics are investigated and compared for cases with and without melt convection. The cases without convection show good agreement with available coarsening theories for a finite fraction of solid. In the cases with flow the mean radius of the solid particles increases at a faster rate than without convection. The ripening exponent changes from 1/3 to 1/2, while the rate constant depends on the fraction of solid. Comparisons are made with the convective ripening theory of Ratke and Thieringer. Although the present analysis of coarsening is hampered by the limited number of particles in the domain, some qualitative results are presented for the effect of convection on the particle radius distribution. Finally, the present simulations allow for a determination of the permeability of the mush as a function of the fraction of solid, and the dependence of the permeability on the ripening kinetics is shown to be scalable using the specific surface area or the mean radius. 相似文献
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F. L. Mota Y. Song J. Pereda B. Billia D. Tourret J.-M. Debierre R. Trivedi A. Karma N. Bergeon 《JOM Journal of the Minerals, Metals and Materials Society》2017,69(8):1280-1288
To study the dynamical formation and evolution of cellular and dendritic arrays under diffusive growth conditions, three-dimensional (3D) directional solidification experiments were conducted in microgravity on a model transparent alloy onboard the International Space Station using the Directional Solidification Insert in the DEvice for the study of Critical LIquids and Crystallization. Selected experiments were repeated on Earth under gravity-driven fluid flow to evidence convection effects. Both radial and axial macrosegregation resulting from convection are observed in ground experiments, and primary spacings measured on Earth and microgravity experiments are noticeably different. The microgravity experiments provide unique benchmark data for numerical simulations of spatially extended pattern formation under diffusive growth conditions. The results of 3D phase-field simulations highlight the importance of accurately modeling thermal conditions that strongly influence the front recoil of the interface and the selection of the primary spacing. The modeling predictions are in good quantitative agreements with the microgravity experiments. 相似文献
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相场法模拟强迫层流对流动法向枝晶的影响(英文) 总被引:1,自引:0,他引:1
采用耦和流场的相场模型,考虑热扰动影响因素,模拟非等温条件下低雷诺数过冷熔体强迫层流对流动法向枝晶生长的影响。以高纯丁二腈(SCN)过冷熔体枝晶生长为例,分析熔体有流动和无流动时二次枝晶形貌差异的原因;研究过冷熔体层流速度、流动法向一次枝晶臂偏转角度和枝晶尖端生长速度之间的关系;推导枝晶尖端前沿熔体流动速度值与枝晶生长时间的理论表达式;定量对比其理论值与模拟值,结果吻合较好。 相似文献
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《Acta Materialia》2000,48(1):43-70
The status of solidification science is critically evaluated and future directions of research in this technologically important area are proposed. The most important advances in solidification science and technology of the last decade are discussed: interface dynamics, phase selection, microstructure selection, peritectic growth, convection effects, multicomponent alloys, and numerical techniques. It is shown how the advent of new mathematical techniques (especially phase-field and cellular automata models) coupled with powerful computers now allows the following: modeling of complicated interface morphologies, taking into account not only steady state but also non-steady state phenomena; considering real alloys consisting of many elements through on-line use of large thermodynamic data banks; and taking into account natural and forced convection effects. A series of open questions and future prospects are also given. It is hoped that the reader is encouraged to explore this important and highly interesting field and to add her/his contributions to an ever better understanding and modeling of microstructure development. 相似文献
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材料科学与工程领域中,相场法是计算材料学的重要分支。相场法在模拟与预测材料微观组织、形貌演化等方面的作用越来越突出。材料微观组织决定其宏观服役性能。商业合金材料性能的改变与控制,在很大程度上依赖于精细调控固态相变过程以期获得理想的微组织图斑。实验对于合金材料固态相变的分析侧重于结果的观测与讨论,对于相变动力学过程研究较少。基于微观扩散理论的相场模型在原子尺度上研究合金固态相变过程,这显著不同于其它的相场模型。本文系统阐述了微观相场模型在合金固态相变方面的研究思路及研究成果。在此基础上,阐述了当前研究的难点,展望了微观相场在固态相变领域的发展前景,最后特别指出了微观相场在合金相变方面未来的研究方向。 相似文献