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采用耦合群体动力学方法与元胞自动机方法建立了细化处理条件下铝合金凝固微观组织演变的数值模型.该模型考虑了a-Al的非均匀形核过程、晶粒的初始球形长大以及之后的枝晶生长过程.利用建立的模型模拟了Al-5Ti-1B中间合金细化工业纯铝凝固组织演变过程.结果表明:形核初始阶段,熔体中存在充足数量的有效形核粒子, a-Al形核率随着熔体过冷度的增大逐渐增高;形核开始不久后, a-Al的异质形核过程由熔体中有效形核粒子数量控制,直到再辉发生,形核停止.模拟分析了中间合金添加量以及熔体冷却速度对工业纯铝凝固组织演变过程的影响,模拟结果与实验结果相符,验证了模型的准确性. 相似文献
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基于充模过程的两相黏弹性流体模型, 采用同位网格有限体积法, 结合浸入边界法和界面追踪的复合水平集流体体积方法实现了带嵌件型腔内充模过程的动态模拟. 基于上述模型和算法模拟了熔体前沿界面及熔接线的动态演化过程, 而且通过线性应力-光学定律得到了熔接线附近的流动诱导应力分布情况; 讨论了熔体温度及模具温度对熔接线区域凝固层厚度的影响. 数值结果表明: 本文提出的方法可用于模拟复杂型腔内的充模过程以及熔接线的自动追踪; 由于聚合物黏弹性熔体流动的复杂性, 当两股熔体相遇后, 熔接线不同位置的应力分布变化较大; 熔体或模具温度越高, 熔接线区域凝固层厚度越薄, 提高熔体或模具温度能够改善甚至消除充模过程中的熔接线. 相似文献
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采用分子动力学方法对Al50Mg50合金熔体的快速凝固过程进行了模拟,并采用双体分布函数、键型指数法和原子团类型指数法等方法,从微观结的不同层面对Al-Mg合金熔体快速凝固过程中微观结构的演化机理进行了深入的分析研究.结果表明:本模拟所获得的Faber-Ziman偏结构因子与实验结果符合较好.Al50Mg50合金熔体具有遗传性,在快速凝固过程形成了非晶态结构,其中二十面体短程序结构对非晶态结构的形成起决定性作用.基于原
关键词:
Al-Mg合金熔体
快速凝固过程
分子动力学模拟
微观结构 相似文献
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采用分子动力学方法对熔体初始温度热历史条件对液态金属Na凝固过程中微观结构的影响,进行了模拟研究,并采用双体分布函数g(r)曲线、键型指数法和原子团类型指数法对凝固过程中的微观结构进行了分析.结果表明:液态金属Na在不同熔体初始温度条件下以1×1011K/s冷速凝固时,均形成晶化结构,其中1661和1441键型或体心立方基本原子团(14 6 0 8)在凝固过程中对微观结构的转变起决定性作用.同时发现:熔体初始温度对凝固微结构有显著影响,而对液态和过冷态的微观结构影响并不明显,只有在晶化起始温度Tc附近才充分地展现出来.不同熔体初始温度对凝固结构的晶化程度有不同的影响,虽其影响程度是随着熔体初始温度的下降呈非线性变化关系的,但仍表明是可以通过改变熔体初始温度来加以控制的.原子团类型指数法(比键型指数法)更进一步表征了晶化体系中原子团的结构特征,将有利于对液态金属凝固过程中微观结构的转变机理进行更为深入的研究. 相似文献
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本文用分子动力学模拟研究了Ni熔体以不同冷速凝固后微观结构的演变规律, 并通过理论计算确定出了Ni熔体凝固后获得理想非晶的临界条件. 模拟结果发现冷速小于1011 K/s时, Ni 熔体凝固后形成晶态组织; 冷速在1011 K/s到1014.5 K/s之间时, Ni熔体凝固后形成由晶态结构与非晶态结构组成的混合组织. 冷速小于1010 K/s, Ni 熔体凝固后形成的晶态组织具有fcc结构; 冷速在1010 K/s到1014.5 K/s之间时, Ni熔体凝固后组织中的晶态由fcc和hcp结构层状镶嵌排列构成. 通过分析模拟结果和计算结果, 确定出了Ni熔体凝固后形成理想非晶的临界冷速为1014.5 K/s. 并发现Ni熔体中临界晶核(冷速等于1014.5 K/s)和亚临界晶核(冷速大于1014.5 K/s) 均由fcc和hcp组成层状偏聚结构, 这表明Ni熔体中生长的晶体、临界晶核和晶胚的结构是相同的.
关键词:
分子动力学模拟
晶体团簇
临界冷速
结构 相似文献
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《物理学报》2016,(24)
基于充模过程的两相黏弹性流体模型,采用有限体积、浸入边界和复合水平集流体体积方法,数值模拟了聚合熔体在复杂型腔中的充模过程.首先,借助一类特殊函数(R-functions)将基于基本几何体的水平集函数组合成描述复杂型腔的形状水平集函数.然后,采用浸入边界法处理复杂型腔问题,有限体积方法求解熔体控制方程,利用复合水平集流体体积方法对熔体前沿界面进行隐式追踪.基于有限伸展非线性弹性哑铃本构方程模型,计算熔体分子构型张量,通过取向椭圆描述分子的取向及拉伸行为,实现了充模过程中分子构型的可视化.最后,对带有两个圆形嵌件的环状型腔内的充模过程进行数值模拟研究,得到了充模过程中型腔内的温度、应力及分子构型的变化情况,并重点分析了充模速度、熔体温度和模具温度等对分子构型的影响.数值结果表明:本文提出的耦合模型可以成功模拟复杂型腔内充模过程中的温度、应力和分子取向等物理量的动态变化;适当提高注射速度可以增大熔接痕的强度;提升熔体温度和模具温度,可以有效改善甚至消除熔接痕. 相似文献
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《物理学报》2016,(22)
基于高阶Taylor展开提出一种改进的光滑粒子流体动力学(CSPH_HT)方法,并试探性地应用于涉及界面变形的黏弹性聚合物熔体充模过程的模拟.首先,针对传统光滑粒子流体动力学(SPH)方法和已有改进SPH方法的缺点,基于高阶Taylor展开,建立了一种新的改进SPH格式.然后通过基准算例验证了新的改进SPH方法的优势.最后,运用改进SPH方法模拟了环形腔和方形腔内的聚合物熔体充模过程,展示了XPP熔体和FENE-P熔体充模过程中界面演化的不同之处,分析了型腔参数对流动的影响.数值结果表明:CSPH_HT方法具有较高的数值精度和较好的数值稳定性,XPP(extended pom-pom)熔体和有限拉伸非线性弹簧(FENE-P)熔体具有不同的流动特性,型腔参数的微小变化能够对流动造成很大影响. 相似文献
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针对合金熔体等液体材料的超声处理过程,选取水作为透明模型材料,采用数值模拟计算和示踪粒子实验方法,研究了20和490 kHz两种频率超声作用下水中的声场和流场分布.结果表明,增大变幅杆半径能够提高水中声压水平,扩大空化效应的发生区域.当超声频率为20 kHz时,水中声压最大值出现在超声变幅杆下端面处,且声压沿传播距离的增大而显著减小.如果超声频率增加至490 kHz,水中的声压级相比于20 kHz时明显提高,且声压沿着超声传播方向呈现出周期性振荡特征.两种频率超声作用下水中的流场呈现相似的分布特征,且平均流速均随着变幅杆半径增大表现出先升高后降低的趋势.变幅杆半径相同时,20 kHz频率超声作用下水中的平均流速高于490 kHz频率超声.采用示踪粒子图像测速技术实时观察和测定了水中的流速分布,发现其与计算结果基本一致. 相似文献
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Shadowgraph and schlieren techniques were used to observe gravity-related flow arising during solidification. The purpose of these studies was to elucidate the results of previous low gravity solidification experiments. Shadowgraph and schlieren techniques were selected as most suitable for operation in the anticipated experimental environment. A laser shadowgraph/schlieren system was built and flown on KC-135 low gravity simulation flights. A solution of ammonium chloride and water was cooled during the experiment, causing solidification. Growth plumes in the solution were observed and photographed using shadowgraph and schlieren techniques. Results are presented and related to previous work. 相似文献
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Phase field simulation of the columnar
dendritic growth and microsegregation in a binary alloy 下载免费PDF全文
This paper applies a phase field model for polycrystalline solidification in binary alloys to simulate the formation and growth of the columnar dendritic array under the isothermal and constant cooling conditions. The solidification process and microsegregation in the mushy zone are analysed in detail. It is shown that under the isothermal condition solidification will stop after the formation of the mushy zone, but dendritic coarsening will progress continuously, which results in the decrease of the total interface area. Under the constant cooling condition the mushy zone will solidify and coarsen simultaneously. For the constant cooling solidification, microsegregation predicted by a modified Brody- Flemings model is compared with the simulation results. It is found that the Fourier number which characterizes microsegregation is different for regions with different microstructures. Dendritic coarsening and the larger area of interface should account for the enhanced Fourier number in the region with well developed second dendritic arms. 相似文献
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实验研究了低频交变电磁场作用下, 7075合金半连铸坯微观组织形貌及各溶质元素的固溶 情况;并就电磁场对液固相线位置和结晶间隔的改变进行了测定;此外还数值模拟了电磁场 对半连铸过程中液穴内部温度场和流动场的影响.从电磁场对7075合金凝固过程中的溶质分 配系数,结晶间隔,液穴内部温度场、流动场以及微观组织形貌的影响出发,尝试性地对电 磁场的强制固溶机理进行探讨性的解释和说明.
关键词:
电磁场
半连铸
铝合金
固溶 相似文献
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Numerical simulation of transient temperature field during laser keyhole welding of 304 stainless steel sheet 总被引:1,自引:0,他引:1
A three-dimensional transient numerical model was developed to study the temperature field and molten pool shape during continuous laser keyhole welding. The volume-of-fluid (VOF) method was employed to track free surfaces. Melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. The enthalpy-porosity technique was employed to account for the latent heat during melting and solidification. Temperature fields and weld pool shape were calculated using FLUENT software. The calculated weld dimensions agreed reasonable well with the experimental results. The effectiveness of the developed computational procedure had been confirmed. 相似文献
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Numerical study of semi-molten droplet impingement 总被引:1,自引:0,他引:1
Due to the low thermal conductivity of ceramics large temperature gradients are present through the powder particles during
plasma spray deposition. As a result the particles often impinge at the substrate in a semi-molten form; which in turn substantially
affects the final characteristics of the coating being formed. This study is dedicated to the novel modelling development
and simulation of a semi-molten droplet impingement. The study examines the impingement process during impact, spreading and
solidification of semi-molten zirconia. The simulation provides an insight to the heat transfer process during impact and
solidification of a semi-molten powder particle and illustrates the freezing-induced break-up mechanism at the splat periphery. 相似文献
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Microstructural properties and evolution of nanoclusters in liquid Si during a rapid cooling process
T. Gao X. Hu Y. Li Z. Tian Q. Xie Q. Chen Y. Liang X. Luo L. Ren J. Luo 《JETP Letters》2017,106(10):667-671
The formation of amorphous structures in Si during the rapid quenching process was studied based on molecular dynamics simulation by using the Stillinger–Weber potential. The evolution characteristics of nanoclusters during the solidification were analyzed by several structural analysis methods. The amorphous Si has been formed with many tetrahedral clusters and few nanoclusters. During the solidification, tetrahedral polyhedrons affect the local structures by their different positions and connection modes. The main kinds of polyhedrons randomly linked with one another to form an amorphous network structures in the system. The structural evolution of crystal nanocluster demonstrates that the nanocluster has difficulty to growth because of the high cooling rate of 1012 K/s. 相似文献