铝硅合金微观组织数值模拟的研究现状及发展趋势北大核心

随着计算材料的发展，数值模拟技术已在铝硅合金凝固过程微观组织的研究中发挥了重要作用。本文就数值模拟技术应用于铝硅合金凝固过程微观组织的形成过程，综述了模拟铝硅合金微观组织形成过程必要的形核与生长模型；着重描述了广泛应用于模拟铝硅合金微观组织形成过程的方法，如元胞自动机法和相场法；最后展望了未来铝硅合金数值模拟技术的发展趋势。     

铸造凝固微观组织模拟研究进展

铸造凝固微观组织模拟是用计算机模拟铸件微观组织的形成过程,以预测铸件的组织结构和性能.本文概述了目前国内外凝固微观组织数值模拟的研究进展、相关基本原理和模型,介绍了采用计算机进行微观组织模拟的几种主要方法,评述了当前所使用的物理数学模型的特点及局限性,指出了该领域目前面临的问题和未来发展趋势.     

合金过冷熔体中枝晶生长的相场法研究进展

相场法作为一种模拟晶粒长大的有效方法,是目前国内外研究的热点。对铸件的凝固组织进行数值模拟,有利于深入理解凝固组织形成机制,预测铸件的凝固微观组织,优化铸件的工艺。概述了目前国内外三维晶粒微观组织数值模拟的研究进展、相关基本原理和模型,以及在模拟过程中常用的计算方法,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。     

金属凝固组织形成的仿真研究

利用Ｍｏｎｔｅ－Ｃａｒｌｏ方法，依据对金属凝固过程的温度场，浓度场的数值模拟和金属结晶过程中的热力学条件，建立了描述金属凝固组织形成过程的宏观－微观耦合模型，对Ａｌ－４．５％Ｃｕ（质量分数）固溶型合金的凝固组织形成过程进行了模拟，结果与实际凝固组织接近。     

用Cellular Automaton模型方法模拟二元合金多晶粒枝晶生长

研究并针对Cellular Automaton凝固组织模拟方法的物理本质、数值计算方法以及在凝固微观组织模拟中的应用进行了探索。并利用Cellular Automaton凝固组织模拟方法，求解了Al-4．5Cu等轴晶多个枝晶同时生长过程。模拟结果和试验结果吻合很好。     

合金凝固组织微观模拟研究进展与应用

凝固组织是连接合金成分与性能的桥梁,准确认识和把握合金凝固微观组织的形成机理、主导因素与控制途径,对凝固组织与性能的优化具有重要意义。近年来凝固过程数值模拟取得了显著进展,元胞自动机(cellular automaton,CA)在合金凝固组织模拟研究方面展现出极大潜力。本文阐述了凝固组织计算中常见的形核模型与特点,对CA法枝晶生长模拟中的关键环节进行了分析和探讨,在此基础上,简要概括了铸造、定向凝固等相关领域凝固组织宏观-微观耦合模型的开发和应用现状,并对凝固组织模拟的发展趋势进行了展望。     

铸件定向凝固微观组织模拟

铸件微观组织模拟研究向定向凝固及单晶方面发展.简介了微观组织模拟的基本思路,引进三维枝晶包膜跟踪模拟理论,它是一种定向凝固的数值微观组织模拟方法,主要用于模拟一些特殊的对缺陷的存在很敏感的零部件.同时给出了用枝晶包膜跟踪法计算的二维凝固模拟结果.     

金属成形过程组织演变的CellularAutomaton模拟技术

结合金属凝固过程的热成形过程的温度场,浓度场,应力应变场等的数值模拟和结晶,再结晶过程中的热力学,动力学条件,建立了金属成形过程组织演变的宏－微观耦合模型,利用ＣｅｌｌｕｌａｒＡｕｔｏｍａｔｏｎ方法。依据建立的模型对Ｋ４１７Ｎｉ基合金叶片的凝固组织形成过程呼热加工过程的再结晶组织进行了模拟。     

铸件凝固过程微观组织模拟新动态

概述了铸件微观组织模拟的几种典型研究方法,着重介绍了用于定向凝固的微观组织模拟方法--三维枝晶包膜跟踪法,同时分析了当前微观组织模拟研究面临的问题.     

双辊连续铸轧凝固过程数学模型的建立及验证

以等价比热容法处理结晶潜热和以假设的流线边界划分网格节点,建立了双辊连铸薄带凝固过程的宏观速度场、传热、溶质传输和凝固组织形成的微观数学模型以及双辊连铸薄带凝固过程的宏观-微观耦合数学模型.同时,以固相率为媒介,采用宏微观不同的网格尺寸和时间步长,实现了宏观模型与微观模型的耦合,并对建立的双辊连铸薄带凝固组织形成的数学模型进行了验证.     

一种ELC-BH钢板退火组织演变的Monte Carlo模拟

基于Monte Carlo方法所建立的退火模型,以一种含Nb的冷轧超低碳高强度烘烤硬化钢板(简称ELC-BH钢板)为研究对象,进行了退火组织演变的模拟和实验研究。结果表明:模拟结果较好地反映了ELC-BH实验板退火组织演变过程,特别是展示了回复阶段再结晶孕育期,证实了该模型的合理性和实用性;考虑升温、亚晶形成、析出相粒子等影响来进一步改进模型,可改善其实用效果。     

Simulation and visualization of recrystallization microstructure after solution treatment

Simulation models for heterogeneous and simultaneous nucleation and random growth of nuclei were developed in terms of the mechanism of recrystallization and Monte Carlo stochastic simulation method. Combining deterministic simulation with stochastic simulation, the simulation and visualization of the reerystallization microstructure of Ti-15-3 alloy after hot compression deformation and solution treatment were realized. Comparison of the simulated results with the experimental ones suggests that the size and distribution of the simulated recrystallized grains agree well with the actual ones. This proves that the obtained statistic equivalent microstructure models are effective. This study is helpful for determining reasonable hot forming process and improving the forming quality.     

Modeling the austenite–ferrite diffusive transformation during continuous cooling on a mesoscale using Monte Carlo method

A Q-state Potts model is adopted to simulate the austenite–ferrite diffusive transformation during continuous cooling in a low carbon steel on a mesoscale with Monte Carlo method. The effects of the interfacial energy and the carbon diffusion on the phase transformation are both taken into account. The consideration of the interfacial energy effect makes the simulated ferrite grains polygonal. To simulate the carbon diffusion during the process of phase transformation, a random jumping based mesocopic diffusion model is developed. In this paper, the evolutions of the microstructure and the carbon concentration field are simulated. The simulation results of the effects of the cooling rate on the volume fraction of the ferrite and the ferrite grain size agree well with the experimental results. The simulation results show that increasing the cooling rate is an effective way to refine the microstructure. This Monte Carlo simulation technique provides a novel way for investigating the diffusive transformation on a mesoscale.     

有限元与Monte Carlo方法耦合的冷轧纯铝板再结晶模拟

利用有限元软件ANSYS模拟的冷轧铝板应力场及其相应的储能场，在假设的介观非均匀储能场基础上，考虑冷轧铝板的宏观能量场的非均匀性，实现了金属变形的有限元方法与Monte Carlo再结晶模拟方法的耦合，有效地模拟非均匀储能场基础上的冷轧铝板再结晶过程，结合现有的理论与实验结果，比较和验证了两个极限储能部位的介观结构拓扑组织和再结晶动力学参数，得到较为理想的结果。     

微量Si和Ag对低Cu/Mg比Al-Cu-Mg合金时效行为及微观组织结构演化的影响

采用计算机模拟与透射电镜相结合研究微量Si和Ag对低Cu/Mg比Al-Cu-Mg合金时效行为和微观组织结构演变的影响.结果表明:微量Si和Ag的添加改变了该合金的时效析出过程,显著增强了合金的时效硬化效应.微量Si的存在导致了合金时效早期Mg原子团簇、Cu-Mg原子团簇弥散化,而微量Ag的添加导致形成大量Mg-Ag原子团簇.微量Si和Ag极大地改变了合金时效早期的原子团簇化过程从而导致了时效过程中微观组织结构的不同演化过程.     

Progress and Application of Microstructure Simulation of Alloy SolidificationEI北大核心CSCD

Solidification structures are the interaction links between the alloy components and their mechanical properties. Scientifically comprehending about the formation mechanisms, dominant factors and control methods in alloy solidification has a significant effect on the structure control and optimization. Dendritic structure is the most frequently observed solidification microstructure of alloys and controlled by heat, solute, melt flow, capillary and many other factors. Modelling and simulating can accurately quantify various phenomena and evolution rules in the process of solidification, thus play an increasingly important role in the design, preparation, processing and performance optimization of alloy materials. Over the past two decades, remarkable progress has been made and various models have been proposed in microstructure simulation during alloy solidification process, such as deterministic method, phase field (PF), Monte Carlo (MC) and cellular automaton (CA). With the advantages of clear physical meaning, easily programming and high calculation efficiency, CA method has been widely applied in the study of solidification structure simulation and exhibits great advantages. Considering the current development level of computer hardware, numerical model and calculation method, microstructure simulation of large components mainly adopts macro-microscopic coupling calculation method, such as CA-FD/FE model. The heat transfer and other multi-physical fields are calculated at the level of coarse mesh, where-as nucleation and dendritic growth are simulated at a much finer grid level. This paper reviews the main models and development of CA method used for nucleation simulation. The key aspects in the simulation of dendritic growth including mean solid-interface interface curvature, growth kinetics and the algorithm for eliminating "pseudo anisotropy" are discussed. Based on this, the development and application status of macro-micro coupling model during casting, directional solidification and other manufacturing fields are summarized. Finally, the existing problems and future tendency for simulation of solidification structures are analyzed.     

Numerical simulation of heat-affected zone microstructure in GMAW

The grain size in the heat-affected zone (HAZ) of workpieces is an important factor for evaluating the welding quality. The Monte Carlo technique of grain growth in the heat-affected zone of alloy is widely used. A finite element model (FEM) was employed to simulate the temperature field of gas metal arc welding (GMAW) ; the data of thermal cycles were used in the Monte Carlo model to calculate the grain sizes in different welding heat inputs. The equation for the relationship between Monte Carlo Step and real time has been estimated using regression analysis. Then mathematics model of the grain growth could be worked out by both the kinetic model and the Monte Carlo model. The dynamic process of grain growth was simulated by the result of the Monte Carlo model. The experimental result was used to prove the validity of this method in simulating of microstructure.     

考虑炉壁温度变化的高温合金叶片定向凝固过程模拟

考虑炉壁温度的变化,基于Monte Carlo射线追踪法建立了高温合金叶片定向凝固过程的温度场计算改进模型.通过法向射线加密提高加热炉炉壁的辐射计算精度,并采用叶片三维有限差分网格和加热炉二维网格混合使用的方法提高计算效率.叶片和炉壁的温度曲线模拟与实验结果吻合良好,改进模型反映了抽拉过程中炉壁温度的变化及其对叶片内部温度分布的影响,提高了叶片温度的模拟精度.     

高温合金叶片定向凝固过程中辐射换热的计算

提出改进型Monte Carlo射线追踪法进行辐射换热计算,通过子空间的划分,并结合定向凝固的特点回避了传统辐射换热计算中角系数的直接计算,节省了计算时间.把该方法嵌入自行开发的三维模拟软件对柱状晶和单晶叶片的定向凝固过程进行了温度场模拟,并对实际叶片凝固过程进行温度场测试,模拟结果与实测结果较好吻合.     

A MONTE CARLO SIMULATION OF THE CVD DIAMOND FILM

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