共查询到20条相似文献,搜索用时 250 毫秒
1.
在二元合金相场模型研究的基础上,进行扩展获得了多元合金相场模型.以Al-Si-Mg三元合金为例,采用该相场模型实现了逼真地模拟多元合金凝固过程的等轴枝晶生长,得到了二次或更高次晶臂生长等复杂的枝晶形貌.随着第三组元Mg含量的减少,枝晶的二次枝晶越发达,枝晶中溶质的偏析越严重,枝晶尖端的生长速率和半径越大,与丁二腈-丙酮体系中枝晶尖端生长速率、半径随溶质浓度变化关系的理论计算和实验结果相符合.另外,枝晶初生晶臂中心的溶质浓度最低,在被二次晶臂包围的界面区域的溶质浓度最高;固液界面区域具有较大的浓度梯度,其中枝晶尖端前沿的梯度最大.
关键词:
相场法
多元合金
凝固过程
枝晶生长 相似文献
2.
The heat transfer in the ultrasonic processing of stainless steel melt is studied in this thesis. The temperature field is simulated when the metal melt is treated with and without ultrasound. In order to avoid the erosion of high temperature melt, ultrasound was introduced from the bottom of melt. It is found that the temperature of melt apparently increases when processed with ultrasound, and the greater the ultrasonic power is, the higher the melt temperature will be; ultrasonic processing can reduce the temperature gradient, leading to more uniform temperature distribution in the melt. The solidification speed is obviously brought down due to the introduction of ultrasound during solidification, with the increasing of ultrasonic power, the melt temperature rises and the solidification speed decreases; as without ultrasound, the interface of solid and mushy zone is arc-shaped, so is the interface of liquid and mushy zone, with ultrasound, the interface of solid and mushy zone is still arc-shaped, but the interface of liquid and mushy zone is almost flat. The simulation results of temperature field are verified in experiment, which also indicates that the dendrite growth direction is in accord with thermal flux direction. The effect of ultrasonic treatment, which improves with the increase of treating power, is in a limited area due to the attenuation of ultrasound. 相似文献
3.
总结比较了多种微观偏析模型,并针对反向凝固工艺实验研究的传热传质现象进行了数值模拟。讨论分析了溶 质的重新分布对宏观凝固传输过程数值模拟的影响,并与实验数据进行了比较,认为微尺度固液相界面上的溶质再分配对 新生相生长的影响不可忽略。 相似文献
4.
5.
基于Ginzberg-Landau理论,发展了一个与WBM模型和KKS模型一致的新相场模型.并利用该相场模型与溶质场耦合计算,以Al-65%Cu合金为例模拟了不同过冷度条件下,二元合金凝固过程的等轴枝晶生长过程.研究过冷度对二元合金等温凝固过程的等轴枝晶生长以及溶质场分布的影响.结果表明:随着过冷度的增大,枝晶的二次枝晶更加发达,浓度Peclet数和枝晶尖端的生长速率增大,而枝晶尖端的曲率半径减小,枝晶前沿的溶质富集现象也更严重;另外,计算结果与Ivantsov理论符合较好.
关键词:
相场法
枝晶生长
溶质场
Ivantsov理论 相似文献
6.
本文采用耦合凝固和熔化效应的二维元胞自动机(cellular automaton, CA)模型,对温度梯度区域熔化(temperature gradient zone melting, TGZM)效应引起的熔池在固液两相区中的迁移现象进行模拟研究.模拟分析了抽拉速度、熔池初始位置、温度梯度和合金成分等因素对TGZM动力学的影响,并将模拟结果与解析模型的预测结果进行比较验证.通过模拟发现,在温度梯度作用下,熔池总是向着高温方向迁移;当抽拉速度低于或高于临界抽拉速度时,熔池朝向移动的液相线或固相线迁移;对于给定的抽拉速度,位于糊状区内临界位置以上的熔池会迁移进入液相,而位于临界位置以下的熔池会逐步靠近固相线.此外,温度梯度越高,合金成分越低,熔池的迁移速度越快. 相似文献
7.
R. Siquieri J. Rezende J. Kundin H. Emmerich 《The European physical journal. Special topics》2009,177(1):193-205
In this work a study through numerical simulation of dendritic growth for the system Fe-Mn under the influence of a forced
flow field is presented. The investigations are based on an extension of the quantitative phase-field approach developed by
Echebarria et. al. Phy. Rev. E 061604 (2004), to simulate the solidification of Fe-Mn under the influence of a forced flow
field. The simulations are performed for isothermal conditions and the investigation concentrates on the effects of forced
flow on the dendrite morphology during the growth dynamics. The effects of forced flow on microsegregation are also discussed. 相似文献
8.
9.
10.
Numerical simulation of dendrite growth and microsegregation formation of binary alloys during solidification process 总被引:1,自引:0,他引:1 下载免费PDF全文
The dendrite growth and solute microsegregation of Fe-C
binary alloy are simulated during solidification process by using cellular
automaton method. In the model the solid fraction is deduced from the
relationship among the temperature, solute concentration and curvature of
the solid/liquid interface unit, which can be expressed as a quadric
equation, instead of assuming the interface position and calculating the
solid fraction from the interface velocity. Then by using this model a dendrite
with 0 and 45 degree of preferential growth direction are simulated
respectively. Furthermore, a solidification microstructure and solute
microsegregation are simulated by this method. Finally, different
Gibbs-Thomson coefficient and liquid solute diffusing coefficient are
adopted to investigate their influences on the morphology of dendrite. 相似文献
11.
In many scientific and engineering problems the solidification of an alloy leads to a highly convoluted crystalline matrix modeled as a thermodynamically controlled reactive porous medium called a mushy layer. We analyze the interaction of an external shear flow with a solidifying mushy layer through a corrugated mush-liquid interface. We find that the external flow can drive forced convective motions within the mushy layer resulting in the formation of a pattern of dissolution and solidification features transverse to the overall flow. Here we seek to lay bare the underlying processes through a systematic comparison of matched asymptotic expansions and numerical solutions. The success of our modeling effort draws substantially upon understanding gleaned from the fluid mechanics of boundary layers and the theory of multi-component solidification. The results have a broad range of implications in geophysics and materials science. 相似文献
12.
A. M. Glenn S. P. Russo J. D. Gorman P. J. K. Paterson 《Micron (Oxford, England : 1993)》2001,32(8):841-850
Aluminium alloy 5182 (AA5182) contains approximately 4.5% Mg as its principal alloying addition, and is most commonly used to make the lid of the aluminium can. With a view to the possible future development of a micro-macro model to describe the casting of this alloy, the effect of grain refinement on the microsegregation of magnesium in industrial rolling ingots of AA5182 has been investigated at three different depths beneath the edge of the ingot (and hence three different cooling rates)—60, 140 and 600 mm. The accuracy with which published microsegregation models are able to predict the solute distribution profile is assessed. It has been found that the magnesium segregation range (Cmax–Cmin) of the grain refined samples actually increases as cooling rate decreases. The range of the non grain refined samples is independent of cooling rate. The solute concentration profiles of the theoretical microsegregation models examined do not correlate well with the experimentally measured profiles. It is concluded that this poor correlation is due to either the effect of post solidification homogenisation or the influence of macroscopic variables during the cast. A more accurate model of post solidification homogenisation is required to assess the relative contribution of each of these factors to the poor correlation. In addition, it is concluded that the measurement of segregation is best done using a combination of EDX mapping and point analysis techniques to locate and quantify the areas of maximum and minimum solute concentration. 相似文献
13.
14.
针对熔化焊过程建立了宏微观耦合模型,模拟了熔池内不同区域凝固过程中随机取向枝晶的竞争生长过程. 通过宏观三维有限元模型计算熔池中瞬态的传热传质过程,利用双线性插值算法将凝固参数传递给微观组织模型. 采用元胞自动机法模拟随机取向的枝晶在熔池凝固条件下的竞争生长过程. 模拟结果表明,所建立的微观模型能够精确模拟任意生长取向的枝晶. 凝固条件中最大温度梯度方向对枝晶竞争过程有明显选择作用,生长方向与最大温度梯度方向相同或接近的枝晶在竞争中具有更大优势. 焊缝中的晶粒组织由枝晶簇发展形成,晶粒组织的形貌演变取决于相邻枝晶簇之间的竞争过程,具有择优取向的枝晶簇会逐渐排挤非择优取向的枝晶簇并最终将其阻挡在凝固组织内部,宏观晶粒的取向与其内部枝晶簇的生长方向并不一定相同. 熔池中心线附近区域在焊接过程中具有更小的温度梯度、更大的凝固速率以及更大的局部冷却速率,凝固后可以获得更加细小的焊缝枝晶组织. 枝晶间距的模拟结果与相应凝固条件下的试验数据符合较好.
关键词:
焊接熔池
枝晶形貌
竞争生长
元胞自动机 相似文献
15.
采用元胞自动机 (cellular automaton, CA) 模型研究了界面能各向异性对二维定向凝固枝晶生长的影响. 模拟结果显示当晶体的择优生长方向与热流方向一致时, 随着界面能各向异性强度的增大, 凝固组织形态由弱界面能各向异性时的海藻晶转变为强界面能各向异性时的树枝晶. 同时, 界面能各向异性强度会影响稳态枝晶尖端状态的选择, 界面能各向异性越强, 定向凝固稳态枝晶尖端半径越小, 尖端界面前沿的液相浓度和过冷度越小. 稳态枝晶生长的尖端状态选择参数与界面能各向异性强度也存在标度律的指数关系, 而枝晶一次间距则受界面能各向异性强度影响较弱. 当晶体的择优生长方向与热流方向呈-40°夹角时随着界面能各向异性强度的增大, 凝固组织形态由海藻晶逐渐转变为退化枝晶, 后又逐渐转变为倾斜枝晶.
关键词:
元胞自动机
枝晶
界面能各向异性 相似文献
16.
Despite the importance of a complete characterization of dendritic patterns in castings, the availability of studies on the development of tertiary dendrite arms is scarce in the literature. In the present study, the tip cooling rate, local solidification time, primary and tertiary dendrite arm spacings have been determined in Pb–Sb alloys castings directionally solidified under unsteady-state heat flow conditions. The alloys compositions experimentally examined are widely used in the as-cast condition for the manufacture of positive and negative grids of lead-acid batteries. The initial growth of tertiary dendritic arms from the secondary branches was found to occur only for a Pb–3.5 wt% Sb alloy at cooling rates in the range 0.4–0.2?K/s, with no evidence of this spacing pattern for Pb–Sb alloys having lower solute content. Tertiary dendritic branches have been observed along the entire casting lengths for alloys of the Pb–Sb hypoeutectic range having compositions higher than 4.0 wt% Sb. It is shown that a power function experimental law with a characteristic ?0.55 exponent is able to characterize the tertiary spacing evolution with the solidification cooling rate for alloys compositions ≥4.0 wt% Sb. The only exception was the Pb–3.5 wt% Sb alloy for which λ 3 exhibited significant lower values when compared with the experimental values obtained for the other Pb–Sb alloys for a same solidification cooling rate. 相似文献
17.
利用多相场模型模拟了液-固两相体系中固相颗粒的粗化过程, 分析了界面润湿性及固相体积分数对粗化指数、粗化速率及颗粒尺寸分布的影响.结果表明, 不同固相体积分数下粗化指数基本不变, 但粗化速率常数及尺寸分布与固相体积分数及界面润湿性密切相关.在完全润湿条件下, 随着固相体积分数的增加, 粗化速率常数逐渐增大; 而非完全润湿条件下, 随着固相体积分数的增加, 粗化速率常数增大速度变缓, 且当润湿性较低、 固相分数较大时, 粗化速率常数还将随体积分数的增加而下降. 此外, 模拟结果表明各种润湿条件下颗粒的尺寸分布均随着固相分数增加而变宽, 分布峰值降低, 但非完全润湿条件下峰值下降变缓.模拟结果为理解不同实验观测结果之间的分歧提供了依据.
关键词:
粗化
相转变
相场法
润湿性 相似文献
18.
19.
20.
Chubin Yang Lin Liu Ning Luo Jun Zhang Baojun Han Gang Liu Hengzhi Fu 《Applied Physics A: Materials Science & Processing》2014,117(4):1971-1975
The single-crystal superalloys with different deviation angle are prepared by using the liquid metal cooling high-temperature gradient directional solidification furnace, and the orientation evolution of single-crystal superalloys under different solidification interface is studied. The results indicate that the increase of the deviation angle will make the planar interface unstable. With the increase of the solidification rate, the growth direction of the crystal will deviate from the direction of heat flow to the preferred orientation direction. Under the developed dendrite crystal growth, the branches of the dendrite will follow the preferred orientation, nearly free from the effect of the heat flow. 相似文献