复合材料增强颗粒与微观孔洞的三维分布特征及相互影响规律

The particle distribution and micro-pore formation are significatnt factors for composite properties and performance. During casting or solidification process of particle reinforced composites, the two-phase interdendritic flow of liquid and particles has important effect on micro-pore formation. The micro-pores also can change the interdentrictic flow and hence influence the particle distribution. In this project,high resolution 3D X-ray computed tomography technology will be applied to inspect the particles for investigation of their spatial distributions including fractions, particle distances, and segregation or clusters. Also the relation of the particle distributions and micro-pore densities, equivalient diameters, spherities will be analyzed. Based on Darcy law, the macro- model of liquid and particle two-phase interdendritic flow will be established, and the micro-model for micro-pore formation with consideration of microstructure formation and two phase Stokes flow will be founded. Hence, the coupled simualtion technology for the macro- and micro- models will be studied. With simulation application and validation, the theories about interplay among particle, interdendritic flow, and micro-pores can be discussed and founded. The scientific merit of project are consisted of the followings: the 3D distributions of particles in composites; study of interdendritic two-phase flow; knowledges and theroies of interaction between interdendritic particle flow and micro-pore formation; multi-scale model and simulation technology of the interaction behavior. The project investigation will provide important theory and technology for fabrication of large composite castings and ingots.

增强颗粒分布和微观孔洞形成是复合材料性能调控的重要方面。复合材料铸造/凝固过程涉及枝晶间液固两相流，影响微观孔洞形成，微观孔洞又改变该两相流从而影响增强颗粒分布。本课题拟采用高分辨三维X射线断层扫描，研究增强颗粒三维分布特征（数量、颗粒距离、团聚大小与颗粒数目），阐明增强颗粒与微观孔洞（数目、等效直径、形状系数）分布特征间的相互关系；建立基于Darcy定律的枝晶间两相流宏观模型，以及耦合组织形成和Stokes两相流的微观孔洞模型，研究两者耦合的模拟方法和技术，通过模拟应用与验证，研究增强颗粒、枝晶间流动、微观孔洞彼此间相互影响行为和规律。创新之处在于：将复合材料增强颗粒分布研究推向三维，开展凝固过程枝晶间两相流研究；揭示枝晶间增强颗粒流动、偏聚与微观孔洞形成间所蕴含的科学规律；建立能描述增强颗粒与微观孔洞相互作用的多尺度模拟方法。为该复合材料大型铸件/铸锭制备提供理论与技术支持。

在金属基复合材料中颗粒增强铝基复合材料最具发展力，主要应用于航空、航天、汽车、高速机械等领域。利用铸造与凝固是该复合材料大型坯锭与构件成形的主要方法之一，增强颗粒分布和微观孔洞形成是复合材料性能调控的重要方面。复合材料铸造/凝固过程涉及枝晶间液固两相流，影响微观孔洞形成，微观孔洞又改变该两相流从而影响增强颗粒分布。本项目按照预定研究计划，对Al-Cu合金及其SiC颗粒增强复合材料进行了不同凝固参数的定向凝固实验，对凝固组织与颗粒分布进行了分析研究，利用上海光源的同步辐射X射线对复合材料定向凝固试样进行了三维断层扫描与重构，分析了增强颗粒与枝晶的分布关系；进行了不同增强颗粒含量和尺寸的SiCp/A356复合材料铸造，并对取样内部微观孔洞完成了高精度（~1μm）三维X射线断层扫描与重构，研究了增强颗粒含量和尺寸对复合材料微观孔洞特征的影响规律；基于二分Kmeans和DBSCAN算法，设计了材料内部粒子团簇聚类计算方法与程序，对上述复合材料增强颗粒和微观孔洞三维分布特征进行了计算，得到了增强颗粒和微观孔洞的团簇特征参数（团簇内数目、团簇内平均距离等）；基于元胞自动机-玻尔兹曼格子法（CA-LBM），建立了复合材料凝固过程微观组织（含微观孔洞）形成的数学模型，提出了颗粒受力、运动及与（枝晶）界面作用的计算方法，基于GPU优化了模拟计算技术，对上述定向凝固实验进行了模拟应用与对比验证，并进一步讨论了凝固过程颗粒与枝晶的动力学行为。项目研究结果丰富了颗粒增强铝基复合材料凝固理论，对该复合材料组织和性能控制具有重要意义。