凝固速率对定向凝固合金DZ22枝晶臂间距和枝晶偏析的影响

采用新研制的超高梯度定向凝固装置，研究了不同凝固速率下定向凝固高温合金ＤＺ２２枝晶臂间距和枝晶偏析。结果表明，冷运速率增大，枝晶臂间距显著细化，枝晶偏析被强烈抑制。当冷运速率为５２．４Ｋ．ｓ＾－１时，一次、二次枝晶臂间距λ１和λ２分别为２８．８和８．４μｍ，Ｎｂ，Ｔｉ，Ａｌ，Ｃｒ，Ｃｏ，Ｗ等元素的偏析比均趋近于１。     

挤压铸造Al2O3/Al-4.5Cu复合材料的凝固组织和偏析的研究

采用挤压铸造法制备了Al2O3短纤维增强Al-4.5Cu复合材料，研究了凝固组织及其偏析现象，结果表明：用挤压铸造法制备的复合材料的组织致密，纤维分布均匀，基体组织细小，纤维与基体间存在明显的界面层，在凝固过程中，α－Al相在短纤维间隙中形核并向纤维表面生长，θ－CuAl2相以Al2O3短纤维为基底非匀质形核；随着预制件温度的升高，纤维表面Cu元素的浓度增大，纤维间隙中的Cu元素的浓度减小，即元素的偏析现象显著。     

Microstructural evolution and microsegregation in directional solidification of hypoeutectic Al−Cu alloy: A comparison between experimental data and numerical results obtained via phase-field model

The objective of the work is focused on predictions of microsegregation, solidification speed, dendritic arm spacings and dendrite morphology by phase-field model. The numerical results were compared with experimental data. The experimental values for cooling rates and effective partition coefficient were adopted during calculations. The results of microsegregation through phase-field model show excellent agreement with the experimental data. Such excellent agreement is because cooling rates, effective partition coefficient and back-diffusion of solute are considered in the model. For solidification speed, the calculation results show good agreement with the experimental data. Tertiary dendritic arm spacing calculated with phase-field model is compared with experimental data. The results show good agreement between them. The dendrite arm spacing varies with position because high cooling rates are responsible for the refinement effect on microstructure. Finally, two-dimensional simulation produced a dendrite that is similar to that found in the experiment.     

三元合金单相凝固路径的统一解析模型

基于合金枝晶凝固微观偏析统一模型,导出一种新的描述三元合金单相凝固路径的解析模型.该模型具有统一性,不仅可涵盖平衡、非平衡和准平衡3种极限凝固路径模式,而且可考虑任意凝固相的反扩散、冷速和枝晶几何形貌等因素的影响.通过对Al-1.0Cu-6.3Mg,Al-1.49Si-0.64Mg和Al-1.49Si-2.90Mg(质...     

抽拉速率跃迁对定向凝固单晶高温合金DD3一次枝晶间距和微观偏析的影响

采用液态金属冷却高温度梯度定向凝固设备.研究了抽拉速率跃迁对单晶高温合金DD3一次枝晶间距和微观偏析的影响.结果表明,单晶高温合金枝晶一次间距表现出明显的历史相关性.当抽拉速率(或生长速率)分别从600和300μm/s跃迁到100μm/s和直接以100μm/s速率生长时,一次间距分别为56.5,86和111.5μm.而生长速率分别从50和100μm/s跃迁到300μm/s和直接以300μm/s速率生长获得的一次间距分别为109,93和70μm.一次间距值与Hunt-Lu模型预测的基本吻合,但实验结果证明其上限与下限的比值λ_1~(max)/λ_1~(min)>2,与Ma Sahm的预测结果一致.成分分析表明,相同稳态条件下枝晶的一次间距变小.偏析也有所降低.     

钢液凝固过程中微观偏析和钛氧夹杂生成的耦合模型

根据钢液凝固时元素的固-液界面的偏析，并结合溶质元素在固、液相中的有限扩散，建立了钢液凝固过程中微观偏析和钛氧夹杂生成的耦合模型，模型计算表明：由于钛氧夹杂的生成，凝固过程中溶质元素的微观偏析程度得到较大抑制；控制适当的氧含量，有利于夹杂物均匀分布；随着冷却速率的增加，夹杂物数量增加，尺寸变小，当控制在目前薄板坯条件下，半径为0．58μm、含量为10^-5量级的夹杂物可弥散分布于钢中，有利于性能的改善。     

U-6%Nb二元合金凝固过程中显微组织与显微偏析的模拟

提出一个改进的计算固相分数的模型,利用该模型及元胞自动机方法根据相图计算将固/液界面区域内固相分数表示为一个一元二次方程,不需假设界面的位置和形状.对U-6%Nb(质量分数)二元合金的凝固组织和显微偏析的模拟结果表明:初始形核部位Nb浓度最高,随着凝固的进行,该部位Nb浓度不断下降;凝固后期晶界区贫Nb,Nb浓度最低可达3%以下.     

Technology of welding and properties of welded joints of new bainitic and martensitic steels with creep-resistant steels

This paper shows the results of welding tests used so far on high-temperature creep resistant steels and new bainitic and martensitic steels. The positive results of this research allowed the elaboration of a welding procedure specification that was ultimately approved by TÜV. This then allowed the SEFAKO Company to attempt welding of the latest generation boiler steels for use under heavy conditions.     

Microsegregation: From Basic Concepts to Complexity in Liquid Crystal Self-Assembly

This review is focused on the basic concepts of microsegregation and a fundamental understanding of the formation of positionally ordered LC phases based on micro- and nanophases, interaction parameters and interfaces. Selected examples were chosen from the actual literature to illustrate the concepts. Microsegregation is the basis of classical LC phases and cybotaxis, and most importantly, it paves the way to a huge number of new LC phases. Beside the distinct modes of micellar packing motifs and liquid quasicrystals formed by self-assembly of dendritic molecules, attention is also focused on the specific effects of rigid anisometric units and polyphilicity. Honeycomb LC phases, vesicular LC phases and mesophases with 3D-lattices lead to enhanced complexity of LC self-assembly.