共查询到19条相似文献,搜索用时 125 毫秒
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流体受迫流动下的柱状枝晶非对称生长 总被引:1,自引:0,他引:1
本文对Cr25-Ni20不锈钢在受迫流动条件下的柱状枝晶生长行为作了研究,结果表明,流体的定向受迫流对柱状枝晶的形貌影响很大,柱状枝晶的一次枝晶主干相互平等且明显细化,而柱状枝晶迎流侧的二次分枝较背流一侧发达,两侧的二次分枝呈不对称生长,但二次分枝始终垂直于一次枝晶主干,受迫流动造成柱状枝晶两侧温度分布的不均匀,是产生柱状枝晶不对称生长的主要原因。 相似文献
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采用相场法模拟了Fe--0.5%C合金等温凝固过程中单个枝晶和多个枝晶的生长, 研究了过冷度、各向异性、界面厚度、晶体取向以及扰动对枝晶形貌的影响, 获得了具有二次分枝的枝晶形貌, 再现了枝晶生长过程及枝晶臂之间的竞争生长. 模拟结果表明: 凝固过程中存在溶质富集和枝晶偏析, 枝晶主干溶质浓度最低, 枝晶臂之间的液相浓度最高. 随着过冷度的增大, 枝晶生长加快且分枝发达; 界面厚度直接影响枝晶的生长速度; 各向异性影响枝晶的形态; 晶体取向与坐标轴方向一致时枝晶优先生长;扰动的加入导致枝晶分枝的形成. 相似文献
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用相场方法模拟Fe-C合金枝晶生长 总被引:2,自引:0,他引:2
采用相场法模拟了Fe-0.5%C合金等温凝固过程中单个枝晶和多个枝晶的生长,研究了过冷度、各向异性、界面厚度、晶体取向以及扰动对枝晶形貌的影响,获得了具有二次分枝的枝晶形貌,再现了枝晶生长过程及枝晶臂之间的竞争生长.模拟结果表明:凝固过程中存在溶质富集和枝晶偏析,枝晶主干溶质浓度最低,枝晶臂之间的液相浓度最高.随着过冷度的增大,枝晶生长加快且分枝发达;界面厚度直接影响枝晶的生长速度;各向异性影响枝晶的形态;晶体取向与坐标轴方向一致时枝晶优先生长;扰动的加入导致枝晶分枝的形成. 相似文献
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研究了非平衡状态下Cu08wt% Cr 亚共晶合金的定向凝固过程。结果表明, 当温度梯度为30℃/cm , 生长速度分别为3μm /s 和30μm /s 时, Cu08w t% Cr 合金呈(α枝晶+ 共晶) 的非平衡凝固组织; 当温度梯度为30℃/cm 时, α枝晶一次间距随生长速度的增大而增大, 这与枝晶一次间距的Hunt模型在低速度段的规律一致, 而与KP模型的规律相反; Cr 纤维的形成主要与液态Cr 的表面张力、Cr 原子在液相中横向扩散能力及α枝晶间Cr 相的生长环境有关,增强Cr 原子的扩散能力,减小α枝晶侧向分枝及其间隙尺寸有助于规则Cr纤维的形成。 相似文献
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晶体取向对镍基单晶高温合金枝状组织的影响 总被引:2,自引:0,他引:2
本文研究了一种镍基单晶高温合金不同晶体取向形成的枝晶组织的变化规律,发现枝晶择优生长方向偏离热流方向时,一次枝晶形态发生明显的变化,二次枝晶分枝出现明显的不对称性。 相似文献
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本文从自由生长和强制生长两个方面着重评述了单相合金枝晶生长的稳态理论新进展。发现稳态理论近年来有两个重要的进展,一是比较好地解决了自由生长枝晶尖端的稳态扩散场问题;另一是理论分析和实验研究的结果都表明,强制生长枝晶一次间距选择一个较宽的容许范围,平均一次间距在这个范围内的具体取值与凝固系统所经历的历史明显相关 相似文献
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改进了模拟枝晶生长常用的二维元胞自动机和有限差分(CA-FD)模型,新模型引入扰动函数来控制二、三次枝晶的生长;在枝晶生长过程中,将溶质浓度明确地分为液相溶质浓度和固相溶质浓度两部分;并在溶质再分配与扩散过程中采用八邻位差分以减少网格形状导致溶质扩散的各向异性。模拟了Al-4%Cu二元合金过冷熔体中,单个和多个等轴晶沿不同择优方向生长及单方向和多方向柱状树枝晶竞争生长过程中的枝晶形貌、液相溶质浓度和固相溶质浓度分布情况。模拟结果表明:扰动的引入能够促使枝晶产生分支,并控制二、三次枝晶的生长速率;液/固相溶质计算模型能够准确地模拟出枝晶生长过程中液/固相溶质分布;此外改进后的模型实现了枝晶沿任意方向的竞争生长。 相似文献
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强磁场下Zn-2 wt.%Cu合金定向凝固的初步研究 总被引:1,自引:0,他引:1
本文进行了10T强磁场下Zn-2wt.%Cu合金的定向凝固的初步研究.结果发现下拉速度较低时,无磁场时晶体以平界面方式生长,而施加磁场则产生带状组织,并且随着磁场的增加带状组织越来越明显,带状组织间距越来越小;当定向凝固速度较高,晶体以枝晶方式生长时,磁场促进枝晶的分枝,并扰乱枝晶规则生长;随定向凝固速度提高,磁场的作用逐渐减弱. 相似文献
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晶体生长中的非稳态演化过程一直是凝固领域人们很少涉及的课题,尤其在胞枝转变之后相当宽范围的亚快速凝固更是少人问津,而非稳态过程对材料最终的组织往往产生在影响,本文采和有机物模拟合金研究了低速及亚快速凝固范围界面形态与一次间距的演化规律,并初步探讨了其演化机制。 相似文献
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《Materials Science & Technology》2013,29(2):181-184
AbstractThe conventional theory of constrained dendrite growth for binary alloys has been extended to multicomponent alloys based on the Calphad method by consideration of solute interactions in each phase. The variable solute partition coefficients and liquidus slopes under different tip undercooling were calculated in detail for a series of Al-Si-Mg alloys. Their influence on the kinetics of dendrite growth was demonstrated quantitatively. The most important microstructure scale, the primary dendrite spacing, was predicted in several Al-Si-Mg alloys. By comparing with the experimental results of former researchers, it is found that the present method coupled with Calphad is a satisfactory way for the prediction of primary dendrite arm spacing. 相似文献
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Unidirectional solidification of pivalic acid (PVA)-ethanol (Eth) mixture was performed to examine whether an allowable range of primary dendrite spacing definitely exists at a given growth velocity and how the range is history-dependent. PVA-0.59 wt pct Eth was unidirectionally solidified in the range of growth velocity 0.5-64 μm/s at the temperature gradient of 2.3 K/ram. Sequential change in growth velocity was imposed to determine the upper and lower limits for the allowable range of stable spacing. An allowable range of the steady state primary spacing was observed at a given growth velocity, and the extent of the range seems to be dependent on the degree to which step-increase or step-decrease in growth velocity is accomplished. As the degree of sequential change in growth velocity increases, the history-dependence of the selection for the primary dendrite spacing tends to disappear. 相似文献
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R.N. Grugel 《Materials Characterization》1992,28(4):213-219
Hypoeutectic Al-Si alloys were directionally solidified under conditions of steady-state growth. Cross-sectional views of the microstructure, i.e., perpendicular to the growth direction, were examined and measurements of the primary dendrite trunk diameters made. The results are presented as functions of growth velocity, composition, and temperature gradient, and evaluated in terms of relevant theory. It is suggested that the primary dendrite trunk diameter is a reliable, or better, a measure of the local solidification conditions during constrained growth than either the conventionally accepted eutectic (λE) or primary dendrite arm (λ1) spacing. 相似文献
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温度梯度对定向凝固Al-4.5%Cu合金一次枝晶间距的影响 总被引:1,自引:0,他引:1
使用5kg坩埚下拉式定向凝固设备,对Al-4.5%Cu合金进行定向凝固试验,研究Al-4.5%Cu合金在不同温度梯度下一次枝晶间距的变化规律。结果表明:在其他凝固参数不变时,随着温度梯度的增大,一次枝晶逐渐变小,细密,挺直,基本呈平行状分布,同时计算的一次枝晶间距值与Hunt模型计算值接近,实验测得的一次枝晶间距的回归曲线为:y=2843478.3x2-70217.4x+543.8。用温度梯度较高的实验值来模拟时,可得到1λ=26.7G-0.5-135.9,一次枝晶间距λ1与G-0.5基本呈线性关系,这和Hunt模型分析结果一致。 相似文献
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Pivalic acid was unidirectionally solidified in a temperature gradient stage. The microstructure parameters; the primary dendrite arm spacing, 1, secondary dendrite arm spacing, 2, dendrite tip radius, R and mushy zone depth, d, were measured for five different growth rates in a constant temperature gradient, G and for five different temperature gradients in a constant growth rate, V. The depending of the microstructure parameters to the solidification parameters (V, G and GV) for pivalic acid were determined by linear regression analyze. The stability constant, * was calculated by using the experimental values of R and V. The results were compared with the previous works. 相似文献
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采用落管无容器处理技术研究了Sb74.7Sn25.3二元过包晶合金的快速凝固,获得的合金粒子直径D介于70~1080μm之间。理论计算表明,随着粒子直径的减小,过冷度和冷却速率均呈指数关系增大,最大过冷度为298K(0.36TL)。研究发现,在自由落体条件下,快速凝固组织由初生Sb固溶体相和包晶SbSn金属间化合物相组成,Sb固溶体相以非小平面和小平面两种生长方式长大。当过冷度增大时,释放的熔化潜热增多,初生相逐渐细化,非小平面初生Sb相由"粗大枝晶"向"碎断枝晶"转变,当D<400μm时,一次枝晶臂显著变短,二次枝晶间距明显减小;同时发生溶质截留现象,初生Sb固溶体相中溶质Sn的固溶度发生了显著拓展,由ΔT=32K时的7.86%(原子分数,下同)线性增大至ΔT=298K时的10.47%。 相似文献
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Wuxiao WANG Bailing JIANG Sen YUAN Wanqi JIE Guangyu YANG 《材料科学技术学报》2006,22(3):311-314
The liquid quenching method was adopted to study the solidification morphology and microstructure of AZglD Mg alloy in semisolid. The results indicate that cooling rate has important effects upon the solidification structures. Under the cooling rate of liquid quenching, primary α-phase grows first by attaching on the original α grains, or independent nucleation and growth. The high cooling rate makes primary α-phase grow in "rags" or dendrite shape. Eutectic solidification is carried out in terms of both dissociated growth and symbiotic growth. The dissociated growth forms rough and large β-phase at grain boundaries, while symbiotic growth forms eutectic of laminar structure. The small liquid pool inside the original α-phase solidifies basically in the same way as that of intergranular liquid, but owing to less amount of liquid phase, the eutectic solidification is mainly carried out in the dissociated pattern. 相似文献
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The directional dendrite growth velocity in the Cu7oNi30 alloy melt undercooled by 90~185 K was measured by high speed cinematography, and compared with the calculated free dendrite growth velocity. It was found that at lower undercoolings the interaction between the adjacent directionally growing dendrites is weak, and there is not marked difference between the velocity of the directionally growing dendrite and that of free dendrite. But with undercooling increasing,the interaction is enhanced due to the decrease of the primary arm spacing, which makes the velocity difference enlarges quickly. 相似文献