元胞自动机法模拟Al-4．5mass％Cu枝晶生长

通过引入溶质再分配、溶质扩散、界面能各向异性和界面曲率,构建了描述合金凝固微观组织形态演变的2D元胞自动机模型。并用该模型研究了Al-4.5mass%Cu合金凝固过程中树枝晶长大过程。结果表明:该模型较好地描述了枝晶生长、晶间和枝晶偏析。凝固过程中的溶质再分配直接影响着树枝晶的生长形貌和微观偏析形成。成份过冷是液/固界面失稳的主要原因,激发二次晶或三次晶产生。二次晶生长是相互竞争的过程,在成分过冷和曲率过冷作用下,二次晶根部溶质富集程度大,出现明显的"颈缩"。在枝晶生长过程中,枝晶间会形成小范围、高溶质浓度的孤立液体区域,形成晶间偏析或点偏析,树枝晶形貌对晶间偏析程度影响较大。在各枝晶臂上,先凝固部分溶质浓度较后凝固部分溶质浓度低,并且中心溶质浓度较边缘处溶质浓度低,形成枝晶偏析,枝晶偏析在枝晶的亚稳态生长阶段更显著。     

等温凝固过程中枝晶生长与枝晶熟化的相场法模拟

采用相场方法模拟了Al-2%Si合金等温凝固中枝晶生长与枝晶熟化过程。结果表明：在枝晶生长初期主要是初生枝晶臂的长大,形成二次或更高次枝晶臂。当侧向分枝生长到边界后,二次枝晶臂停止生长,从而进入熟化阶段。枝晶的等温熟化模式主要是小枝晶臂的熔化、枝晶臂的合并与熔断,枝晶分枝的平滑化以及小液滴的圆滑化。当凝固时间小于0.7ms,固相分数增加的快,枝晶的生长成为主导;当凝固时间大于0.8ms,固相分数变化不明显,枝晶的熟化成为主导.     

基于元胞自动机法的铝合金定向凝固过程微观组织数值模拟

基于溶质扩散和界面能的作用,考虑成分过冷、曲率过冷和界面能各向异性和界面扰动,并改进了溶质再分配的算法以及界面液相浓度偏导数的离散格式,建立了凝固过程中晶体的生长模型。利用此模型并采用元胞自动机方法对铝合金定向凝固过程中的平界面、胞状和枝晶状三种典型界面形貌演化进行了模拟,并把模拟参数和模拟结果与经典凝固理论进行了比较,发现在G/V值略小于成分过冷判据给出的临界值时就已经获得平界面。并验证了平均一次枝晶间距与温度梯度和抽拉速度的变化关系,与理论结果吻合较好。     

扩散控制的强制性枝晶凝固

本文对SCN基模型合金和金属合金Al—Cu进行了强制性枝晶生长的实验研究,测量并讨论了枝晶端部温度、枝晶端部溶质成分和有效溶质分配系数及其变化规律。分析了强制性枝晶生长过程的扩散传输,指出强制性生长动力学机制受控于枝晶端稳定性行为。实验结果进一步揭示了强制性枝晶凝固的规律。     

Mg含量对Al-Cu-Mg合金定向凝固组织的影响

建立模拟多元合金树枝晶生长的三维元胞自动机模型,耦合合金热力学和生长动力学计算,模拟预测Al-Cu-Mg合金定向凝固组织形成过程,考察Mg含量对定向凝固一次枝晶间距的影响。结果表明,在相同凝固条件下,定向凝固一次枝晶间距随着Mg含量的增加而增大,定向凝固二次枝晶间距随着Mg含量的增加而减小。     

铝合金元胞自动机-有限单元法微观组织模拟

利用有限元商业软件CALCOSOFT2D中的元胞自动机模型,模拟了Al-Si(w(Si)=7%)合金的凝固组织的演变过程,形核模型采用基于高斯分布的连续性形核模型,枝晶尖端生长速度与局部过冷度的关系采用KGT模型.探讨了形核参数、冷却条件等参数对枝晶模拟结果的影响,得到了不同情况下的枝晶演变组织,结果显示能合理反映实际金属凝固物理过程.     

强磁场对丁二腈定向生长形貌的影响

在无磁场以及1T磁场强度条件下,对纯度为99.927%的丁二腈定向凝固过程的生长形貌进行实时观察,通过测量不同试验条件下丁二腈的生长速度、一次枝晶间距、尖端半径等主要特征参数,对磁场下丁二腈定向凝固过程所受的影响进行了理论分析。在无磁场条件下,随着温度梯度的增大,丁二腈模拟金属定向凝固组织为斜枝晶;生长速度几乎不受影响;一次枝晶间距和二次枝晶臂间距减小;生长尖端半径增大。温度梯度不变时,对丁二腈施加磁场强度为1T的磁场,此时丁二腈生长形貌依旧为斜枝晶;生长速度降低;一次枝晶间距普遍增大;生长尖端半径增大。     

强磁场对定向凝固丁二腈枝晶生长速度的影响

在不同磁场强度和不同温度梯度条件下,对纯度为99.927%的丁二腈定向凝固时的生长过程进行实时观察。测算不同实验条件下丁二腈的枝晶生长速度,同时对固液界面的温度变化进行测量。在磁场强度和温度梯度不变时,随着时间的推移,枝晶生长速度逐渐减慢;在磁场强度不变的条件下,随着温度梯度的增大,丁二腈枝晶生长速度加快;温度梯度不变时,随着磁场强度的增大,丁二腈枝晶生长速度减慢。枝晶生长速度发生变化的原因是磁场环境影响了丁二腈枝晶生长的凝固过冷度和吉布斯自由能,枝晶生长的驱动力受到影响,因此枝晶生长速度发生变化。     

纯铜在凝固中微观组织演化的模拟

利用连续准瞬时形核模型和CA模型，结合凝固过程中传热、枝晶尖端生长动力学等因素作用，建立了一个二维元胞自动机模型，并根据这个模型模拟了纯铜铸件在凝固过程中形核、生长的微观过程．将模拟结果与实际组织进行比较表明，该模型可以近似地描述纯铜的凝固组织。     

铝硅合金凝固组织的数值模拟

通过热焓法处理结晶潜热的二维不稳定热传导方程模拟凝固温度场，利用Scheil模型模拟质量浓度场，提出了枝晶尖端生长动力学修改模型，在温度场模拟与质量浓度场模拟基础上模拟了凝固过程中铝硅合金的组织在计算机上实现了组织形成过程的可视化，模拟结果与实验结果进行比较，两者基本吻合。     

Modeling the dendritic evolution and micro-segregation of cast alloy with cellular automaton

In order to precisely describe the dendritic morphology and micro-segregation during solidification process, a novel continuous model concerning the different physical properties in the solid phase, liquid phase and interface is developed. Coupling the heat and solute diffusion with the transition rules, the dendrite evolution is simulated by cellular automaton method. Then, the solidification microstructure evolution of a small ingot is simulated by using this method. The simulated results indicate that this model can simulate the dendrite growth, show the second dendrite arm and tertiary dendrite arm, and reveal the micro-segregation in the inter-dendritic zones. Furthermore, the columnar-to-equiaxed transition (CET) is predicted.     

Modeling of dendritic growth in the presence of convection

In materials science, dendritic growth is the ubiquitous form of crystal growth ob-served in casting and welding of many metals and alloys. The solidified dendritic mor-phology will generally play a key role in the determination of mechanical properties of solid materials. Thus, understanding and control of dendritic growth are crucial in order to predict and achieve desired microstructures and hence, mechanical properties of cast-ing metals and alloys[1]. Dendritic growth is a complicated phy…     

Modeling solidification structure evolution and microsegregation under pressure condition

1. IntroductionPressure casting is widely used in many domains,such as nonferrous alloy casting and special shapecasting. In general, there are two kinds of pressurecasting, one is low-pressure casting, and the other ishigh-pressure casting. Solidificatio…     

Modeling of Microstructure Evolution during Directional Solidification Process

A model was presented to describe the microstructure evolution during the directional solidification process. In this model, the problem of different properties in the solid and liquid phase was solved by making the properties continuous at‘the solidlliquid inteorace. Furthermore, a random noise was incorporated to reflect the anisotropic growth. Moreover, the averaging solute conservation was developed to keep the total solute conservation in the inteorace region. A simple ingot was simulated by this method, the model can represent the micro-structure evolution, solute concentration redistribution, micro-segregation and the columnar-to-equiaxed transition.     

一种合金枝晶凝固微观溶质再分布统一模型

简要概述了合金枝晶凝固微观偏析解析模型化研究进展。基于对具有任意枝晶形貌及任意固相反扩散(SBD)效应的合金凝固过程中微观/宏观溶质传输行为模型化,提出了微观溶质再分布新模型,并进行了不同凝固速率、不同枝晶形貌及SBD效应的Al-4.5％Cu合金与Fe-0.5％C基碳素钢枝晶凝固的模型对比计算。研究表明,所建模型具有包含多种影响因素与统一性的特点,以及模型计算的可行性与有效性。     

Simulation of faceted dendrite growth of non-isothermal alloy in forced flow by phase field method

Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.     

Microstructure evolution of cast Al-Si-Cu alloys in solution treatment

To develop a software to predict the evolution of microstructure and the development of mechanical properties during the heat treatment of cast aluminum alloys, we modeled the redistribution of solute during the solution treatment of multicomponent alloys. The predictions of solidification simulation software or the results of experiment provided the initial microstructure and solute distribution for simulation of heat treatment. Binary through quinary aluminum alloys with silicon, copper, magnesium, and iron were modeled. The basic model assumed local equilibrium （no undercooling due to nucleation or growth） and computed diffusion in the solid constituents during solidification. The evolution of microstructure during solution treatment was followed by qualitative and quantitative metallography. The results of simulation for the ternary alloy Al-7%Si-3.5%Cu were compared to experimental observation.