反应热压(Al_2O_3+TiB_2+Al_3Ti)/Al 复合材料的组织形成机制

Microstructure formation mechanism of (Al_2O_3+TiB_2+Al_3Ti)/Al composites fabricated by reaction hot pressing

采用B或B2O3、TiO2和Al粉反应热压制备了原位(Al2O3+TiB2+Al3Ti)/Al复合材料,采用光学显微镜、扫描电镜和透射电镜分析了原位复合材料的显微组织。热压状态下,反应生成相Al3Ti呈大块不规则形状,尺寸约几十微米;Al2O3和TiB2为细小弥散质点,TEM分析发现TiB2颗粒呈六边形,而Al2O3颗粒呈等轴状。在以Al粉、TiO2粉和B粉为原料制备的复合材料中,除反应生成了大块的Al3Ti相外,还有细小针状Al3Ti相沉淀析出,且呈弥散分布。热挤压后大块的Al3Ti被破碎成细小弥散质点。Al2O3在TiO2和B2O3粉末表面生成;TiB2在B或B2O3粉表面形成,因而均呈弥散分布,且尺寸细小。自TiO2中还原出的Ti溶入液态Al中形成Al3Ti时,Ti可在液态Al中长距离扩散,因而Al3Ti呈大块不规则状。

Two (Al_2O_3+TiB_2+Al_3Ti)/Al composites were made from Al-B_2O_3-TiO_2 and Al-B-TiO_2 raw powders by hot pressing. The microstructure of the two composites was analyzed by OM, SEM and TEM. The results show that coarse Al_3Ti blocks with size of several tens of micrometers are formed during hot pressing, and the fine equiaxed Al_2O_3 and hexagon TiB_2 particulates are formed simultaneously. On the other hand, there are fine Al_3Ti precipitates in the composite fabricated from Al, B and TiO_2 powders. After extrusion, the coarse Al_3Ti blocks are broken into small pieces. Al_2O_3 particles are formed on the surface of TiO_2 or B_2O_3 powder, TiB_2 particles are formed on B or B_2O_3 powders, and they are fine and dispersively distributed. The formation of coarse Al_3Ti block is resulted from long-distance diffusion of Ti in liquid Al.