共查询到20条相似文献,搜索用时 140 毫秒
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《中国新技术新产品》2016,(15)
多相合金凝固过程微观组织的模拟长期以来一直引起不同领域学者的广泛关注和研究,归根结底是因为其在工程应用及理论研究等方面都具有很大的价值。21世纪,计算机及电子科学技术异军突起,并得到全面发展和进步,所以研究多相合金凝固过程微观组织模拟除了可以应用传统研究方法,也可以适时地去应用计算机数值模拟方法,而且随着技术的进步,这方面的研究已经取得了长足的进步,尤其是在凝固应力场,温度场等各种场效应的数值模拟初见成效后,微观组织模拟研究有了新的发展方向和突破口。采用元胞自动机方法对比其他研究方法,对于研究凝固的各种结构模型有以下优点:将固液界面两侧的锐变转化为界面胞元固相份数的渐变,既坚持了尖锐界面的基本假设,又避免了跟踪复杂的固液界面。而且研究时所应用的模型不仅考虑了成分过冷、曲率过冷、界面能各向异性,还考虑到了界面扰动等影响枝品生长的各种不同外界影响因素。 相似文献
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数值模拟可以高效、有针对性地对金属激光选区熔化成型过程中的温度场、熔池形状、残余应力和变形、凝固过程微观组织演变等过程建立相应的模型并对成形件的相关性能做出准确预测,为工艺优化提供科学的依据,显著降低工艺开发成本和缩短工艺开发周期,有力推动金属增材制造向工业级应用的转变。本文综述了金属激光增材制造过程中温度场、熔池动力学、成形件内部残余应力和变形、显微组织变化4个方面数值模拟的最新研究进展,概述了金属SLM过程数值模拟所取得的最新进展,分析了金属SLM数值模拟领域的研究热点和所存在的计算时间长、成本高等问题,最后提出金属SLM过程数值模拟应将3D打印过程中快速凝固、微熔池等特征与大数据、人工智能、深度学习等技术相结合,进一步提高数值模拟精度,拓宽金属激光增材制造加工窗口,为个性化产品开发提供指导。 相似文献
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基于枝晶生长的基本传输过程和元胞自动机(Cellular Automaton,简称CA)-有限元(Finite Element,简称FE)模型基本原理,建立了适应双辊连续铸轧纯铝薄带工艺特点的凝固过程形核和晶体生长的数学模型.模型耦合了宏观温度场和微观组织模拟计算,考虑了溶质扩散、曲率过冷和各向异性等重要因素的影响,定义了界面单元捕获规则,能够模拟凝固过程中枝晶生长的形态.应用本模型对双辊连续铸轧纯铝薄带凝固过程中等轴晶生长、等轴晶多晶粒生长及柱状晶生长、柱状晶向等轴晶演化进行模拟并与实验结果进行对比,模拟结果与实验结果吻合较好,验证了模型的正确性. 相似文献
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《Current Opinion in Solid State & Materials Science》2016,20(1):25-36
We summarize recent advances in modeling of solidification microstructures using computational methods that bridge atomistic to continuum scales. We first discuss progress in atomistic modeling of equilibrium and non-equilibrium solid–liquid interface properties influencing microstructure formation, as well as interface coalescence phenomena influencing the late stages of solidification. The latter is relevant in the context of hot tearing reviewed in the article by M. Rappaz in this issue. We then discuss progress to model microstructures on a continuum scale using phase-field methods. We focus on selected examples in which modeling of 3D cellular and dendritic microstructures has been directly linked to experimental observations. Finally, we discuss a recently introduced coarse-grained dendritic needle network approach to simulate the formation of well-developed dendritic microstructures. This approach reliably bridges the well-separated scales traditionally simulated by phase-field and grain structure models, hence opening new avenues for quantitative modeling of complex intra- and inter-grain dynamical interactions on a grain scale. 相似文献
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Complicated morphologies of directional solidification structures attract a lot of theoretical studies and commercial uses.
As known, the boundary heat flux has an important significance to the microstructures of directional solidification. In this
article, the interface evolution of directional solidification with different boundary heat fluxes is discussed. In this study,
only one interface has heat flow, and Neumann boundary conditions are imposed at the other three interfaces. From the calculated
results, it is found that different heat fluxes cause different microstructures in the directional solidification. When the
heat flux equal to 18 W/cm2, the growth of lengthways side branches is accelerated and the growth of transverse side branches is restrained. At the same
time, there is dendritic remelting in the calculating domain. When the heat flux equal to 36 W/cm2, the growth of the transverse side branches and the growth of the lengthways side branches compete with each other. When
the heat flux equal to 90 or 180 W/cm2, the growth of transverse side branches absolutely dominates. The temperature field of dendritic growth is also analyzed
and the relation between heat flux and temperature field is found. 相似文献
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In the present article, evolution of microstructure during solidification, as a function of various parameters, is discussed.
Macrosegregation is described as being due to insufficient diffusivity of solute in the solid. Pattern formation is discussed
in the light of instabilities at the solidification growth front. An overview of the scaling relations for various microstructures
is given. Metastable extensions to equilibrium phase diagrams and corrections to equilibrium quantities are described. 相似文献
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A two-dimensional(2-D)multi-component and multi-phase cellular automaton(CA)model coupled with the Calphad method and finite difference method(FDM)is proposed to simulate the gas pore for-mation and microstructures in solidification process of hypoeutectic Al-Si-Mg alloys.In this model,the pore growth,and dendritic and eutectic solidification are simulated using a CA technique.To achieve the equilibrium among multiple phases during ternary Al-based alloy solidification,the phase transition thermodynamics and kinetics are evaluated by adopting the Calphad method.The diffusion equations of hydrogen and two solutes are solved by FDM.The developed CA-FDM coupled model can be used for sim-ulating the evolution of gas microporosity and microstructures,involving dendrites and irregular binary and ternary eutectics,of ternary hypoeutectic Al-Si-Mg alloys.It has the capability of reproducing the interactions between the hydrogen microporosity formation and the growth of dendrites and eutectics,the competitive growth among the growing gas pores of different sizes,together with the time-evolving concentration fields of hydrogen and solutes.The simulated morphology of gas pore and microstructure has a good agreement with the experimental observation.The influences of the initial hydrogen concen-tration and cooling rate on the microporosity formation are investigated.It is found that the main portion of porosity formation occurs in the eutectic solidification stage through analyzing the profiles of porosity percentage and solid fraction varying with solidification time.The varying features of simulated porosity percentage,the maximum and average pores radii indicate that increasing initial hydrogen concentration promotes the formation of higher final porosity percentage and larger pores,while the size of gas pores will significantly reduce with increasing cooling rate,leading to a lower final porosity percentage. 相似文献
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《材料科学技术学报》2020,(4)
The morphological instability of solid/liquid(S/L) interface during solidification will result in different patterns of microstructure. In this study, two dimension(2 D) and three dimension(3 D) in-situ observation of solid/liquid interfacial morphology transition in Al-Zn alloy during directional solidification were performed via X-ray imaging. Under a condition of increasing temperature gradient(G), the interface transition from dendritic pattern to cellular pattern, and then to planar growth with perturbation was captured. The effect of solidification parameter(the ratio of temperature gradient and growth velocity(v), G/v) on morphological instabilities was investigated and the experimental results were compared to classical "constitutional supercooling" theory. The results indicate that 2 D and 3 D evolution process of S/L interface morphology under the same thermal condition are different. It seems that the S/L interface in 2 D observation is easier to achieve planar growth than that in 3 D, implying higher S/L interface stability in 2 D thin plate samples. This can be explained as the restricted liquid flow under 2 D solidification which is beneficial to S/L interface stability. The in-situ observation in present study can provide coherent dataset for microstructural formation investigation and related model validation during solidification. 相似文献
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《Science and Technology of Advanced Materials》2001,2(1):117-126
Microstructure evolution in equiaxed dendritic solidification is investigated through the study of free dendritic growth in a supercooled melt. A detailed measurement of microstructural features (such as side-branch spacings, envelope shape, projection area, and contour length) of freely growing succinonitrile dendrites is performed using images from the microgravity experiment of Glicksman and co-workers. The measurements show that the microstructure evolution of an equiaxed dendrite is divided into two regimes: an initial linear regime and a subsequent non-linear coarsening regime. It is found that unique scaling relations exist between the measured geometry parameters and the primary tip radius or speed for both regimes. The underlying mechanisms involved in dendritic structure evolution are discussed. In addition, using the phase-field method, we perform numerical experiments to investigate the effects of melt convection on equiaxed dendritic growth. The dendrite tip operating state (i.e. the tip velocity and radius) is quantitatively evaluated as a function of the flow velocity and dendrite orientations and compared with Microscopic Solvability Theory. Other structural features (such as the side-branches) of an equiaxed dendrite in the presence of flow are also examined in order to show how convection influences microstructure evolution in equiaxed dendritic growth. 相似文献
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Microstructure evolution in equiaxed dendritic solidification is investigated through the study of free dendritic growth in a supercooled melt. A detailed measurement of microstructural features (such as side-branch spacings, envelope shape, projection area, and contour length) of freely growing succinonitrile dendrites is performed using images from the microgravity experiment of Glicksman and co-workers. The measurements show that the microstructure evolution of an equiaxed dendrite is divided into two regimes: an initial linear regime and a subsequent non-linear coarsening regime. It is found that unique scaling relations exist between the measured geometry parameters and the primary tip radius or speed for both regimes. The underlying mechanisms involved in dendritic structure evolution are discussed. In addition, using the phase-field method, we perform numerical experiments to investigate the effects of melt convection on equiaxed dendritic growth. The dendrite tip operating state (i.e. the tip velocity and radius) is quantitatively evaluated as a function of the flow velocity and dendrite orientations and compared with Microscopic Solvability Theory. Other structural features (such as the side-branches) of an equiaxed dendrite in the presence of flow are also examined in order to show how convection influences microstructure evolution in equiaxed dendritic growth. 相似文献