中文摘要：

采用激光区熔定向凝固技术制备了A12O3／Y3A15O12（YAG）共晶自生复合材料．利用SEM，XRD，EDs及TEM对共晶形貌特征、相组成、界面结构．组织演化及相析出规律进行了研究；利用分形维数对非规则微观组织形态进行了定量表征．在此基础上，分析讨论了氧化物共晶的非规则共晶生长机制．结果表明：A12O3／YAG共晶自生复合材料由无规则均匀分布的A12O3和YAG两相组成，两相之间相互交错，耦合生长，呈象形文字结构；凝固过程中，YAG相作为领先相析出；随扫描速率增大，共晶间距高度细化，最小层间距为0．2μm；在低扫描速率下，共晶组织属典型的层片状非规则共晶组织，具有明显的分形特征，当扫描速率达到2000μm／s时，出现胞状和树枝状组织，组织分形特征减弱；共晶两相高的熔化熵及激光快速凝固大的动力学过冷导致的小平面／小平面共晶生长是形成复杂非规则共晶组织的主要原因．

英文摘要：

Directionally solidified A12O3/YaA15O12（YAG） eutectic in situ composite was fabricated by the laser zone remelting technique. The eutectic morphology, phase composition, interface structure, microstructure evolution and phase precipitation rule were analyzed by SEM, XRD, EDS and TEM. The irregular microstructure morphology was quantitatively characterized by fractal dimen- sion, and the irregular growth mechanism of the oxide eutectic was discussed. The results show that the composite only consists of homogeneously distributed A12O3 and YAG phases with well matched interfaces, which interweave each other and grow coupledly, showing a “Chinese script” structure. The YAG phase is the primary phase during solidification. The eutectic spacing is highly refined with increasing the laser scanning rate and the minimal spacing is down to 0.2μm. At low rate, the eutectic tends to show typical lamellar irregular eutectic structure and has evident fractal characteristic, whereas, when the rate reaches a high value of 2000μm/s, the cellular and dendritic structures appear and the fractal characteristic is weaken. The faceted/faceted eutectic growth derived from the large kinetic undercooling of laser rapid solidification and high entropies of fusion of eutectic phases is the most factor to form the complexly irregular eutectic morphology.