共查询到19条相似文献,搜索用时 687 毫秒
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从定向凝固界面形的非稳态分析出发,对单相凝固亚结构的几个特征尺度包括平界面失稳初始扰动波长、胞晶间距、枝晶一次间距、枝晶尖端半径及二次间距与两有态转变即胞枝转变和高梯度绝对稳定性进行了实验研究和理论分析。 相似文献
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液固相变中的界面形态选择 总被引:3,自引:0,他引:3
在凝固过程中,液固界面形态经历了从平面向胞状进而树枝晶,然后又向针状胞直至绝对稳定平界面的演泽过程。本文以理论分析与实验结果为基础,讨论了液固 界面稳定性与界面形态的关系和生长速率的影响。阐明亚快凝固段生长形成的超细柱晶组织特性及其应用前景。 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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本文研究了凝固速率对单晶高温合金凝固界面形态,合金元素含量、r'相及r/r'相界面结构的影响。结果表明,随凝固速率的减小,凝固界面从细枝、粗枝向胞状、平面转变,r'形成元素挥发严重,弥散分布的r'相含量减少,r'相严重合并粗化,r/r'相界面失去共格,亚晶界量减少。 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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Xin Lin Yanmin Li Zhengxia Liu Tao Li Weidongo Huang 《Science and Technology of Advanced Materials》2013,14(1):293-296
A self-consistent model is developed to describe the morphology evolution during unidirectional solidification, which shows that, for a given temperature gradient, the interface morphology will go planar → shallow cell → deep cell → dendrite → cell → planar with increasing growth velocity. By examining the interaction of adjacent cells/dendrites, a wide allowable range of primary spacing for given growth conditions is determined, which shows a good agreement with experimental results. Numerical results show that cellular/dendritic and dendritic/cellular transitions appear not at a unique velocity but over a range of velocities, the critical velocity for the transition being dependent on the primary spacing before the transition. 相似文献
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《材料与设计》2015
Solidification samples of undercooled Co–24 at%Sn eutectic alloy containing a small amount of Mn (<1.0 at%) were prepared by the glass fluxing technique. The surface and internal solidification microstructures of the samples were observed by a scanning electron microscope (SEM) and an optical microscope (OM), respectively. The experiment results revealed that the addition of 0.5 at%Mn remarkably changed the solidification behaviors of the undercooled Co–24 at%Sn eutectic alloy. The addition of 0.5 at%Mn influenced the morphological selection of eutectic growth interface by increasing the interface energy anisotropy during the solidification of the undercooled Co–24 at%Sn eutectic melt. As undercooling increases, the coupled eutectic growth interface morphology successively experienced dendritic pattern, factual seaweed pattern and compact seaweed pattern. Besides, the addition of 0.5 at%Mn decreased the critical undercooling for the formation of anomalous eutectic by introducing a new formation mechanism of anomalous eutectic, i.e. divorce eutectic mechanism. 相似文献
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《Science and Technology of Advanced Materials》2001,2(1):293-296
A self-consistent model is developed to describe the morphology evolution during unidirectional solidification, which shows that, for a given temperature gradient, the interface morphology will go planar→shallow cell→deep cell→dendrite→cell→planar with increasing growth velocity. By examining the interaction of adjacent cells/dendrites, a wide allowable range of primary spacing for given growth conditions is determined, which shows a good agreement with experimental results. Numerical results show that cellular/dendritic and dendritic/cellular transitions appear not at a unique velocity but over a range of velocities, the critical velocity for the transition being dependent on the primary spacing before the transition. 相似文献
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Nathalie Bergeon Anthony Ramirez Liang Chen Bernard Billia Jiho Gu Rohit Trivedi 《Journal of Materials Science》2011,46(19):6191-6202
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Transient growth conditions are common to a variety of technical solidification processes and lead to modified materials properties. In directional solidification the microstructure at the solid-liquid interface of an alloy is a result of the interaction of diffusive and convective heat and mass transport in the bulk and of interface and thermophysical properties. We have carried out experiments under diffusive conditions without convection in microgravity during the sounding rocket missions TEXUS-36 and 40. The used transparent alloy succinonitrile-acetone freezes like metals and the solidification process was observed in-situ. Within a gradient furnace the solid-liquid interface is forced to move accelerated and to transform from planar into cellular and dendritic structures. The dynamics of the planar interface and of the spacing and the amplitude of diffusive grown cells and dendrites were observed directly with cameras and analyzed. A comparison of the TEXUS-40 results to predictions taken from a macroscopic thermal model, a coupled heat-mass transfer model and a phase-field model was carried out. A good agreement is found for the planar interface dynamics for the coupled heat-mass transfer model and the phase-field model, when using additional information from the thermal modelling. In the cellular and dendritic growth regime typical microstructure features can be reproduced by the phase-field model. The experimental results thus serve as important bench-marks for the validation of numerical models describing time-dependent solidification processes. 相似文献
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The effect of solid/liquid intedece morphologies on the microstructure and segregation of a new type superalloy, DSX40M, was studied. It has been found that the primary arm spacing presents maximum value as the solid/liquid interface shape transforms from cellular to cellular-dendritic.As the alloy solidifies with a coarse dendritic interface, the solute segregation degree and the average size of the carbide reach the maximum values because of the widest mushy zone. A Zr-rich phase forms at this range. Within the solidificatin rate range of dendritic interface. the primary dendritic arm spacing and solute segregation decrease with the increasing of solidification rate and the Zr-rich phase disappears. It should be indicated that the change of the solid/liquid interface does nt vary the carbide type, but greatly affects the average size of the carbides.The quantitative results of the carbide size change in this alloy system with different solid/liquid interfaces is presented 相似文献