原位合成钛基复合材料增强体TiC的微结构特征

Microstructural characterization of TiC in in situ synthesized titanium matrix composites

利用钛与石墨之间的自蔓燃高温合成反应经普通的钛合金铸造工艺制备了TiC增强的钛基复合材料。借助X射线衍射仪、光学金相显微镜和透射电镜分析了钛基复合材料的物相组成和增强体的微观结构。结果表明 :复合材料由TiC增强体和基体钛合金组成。TiC显示两种不同的形态 :树枝晶状和等轴或近似等轴状。原位合成的增强体TiC以溶解析出的方式生长。从二元相图分析 ,凝固过程经历三个阶段 :初晶TiC ,二元共晶 β Ti+TiC和固态相变。由于成分过冷的形成 ,初晶TiC以树枝晶的形态生长。二元共晶TiC以等轴或近似等轴状生长。少量的TiC在形核与长大的过程中形成孪晶结构 ,孪晶面是 (111)

TiC reinforced titanium matrix composites were produced by non-consumable arc-melting technology utilizing the self-propagation high-temperature synthesis (SHS) reaction between titanium and graphite. X-ray diffraction (XRD) was used to identify the phases in the composites. Microstructures of the composites were observed with optical microscope (OM) and transmission electron microscope (TEM). The results show that there are two phases in the composites: TiC and titanium matrix alloy. TiC shows two different shapes: dendritic shape, equiaxed or near-equiaxed shape. The in situ synthesized TiC grows in a way of dissolution-precipitation. Analysis of binary phase diagram determined that the solidification path undertook the following three stages: primary TiC, binary eutectic β-Ti+TiC and solid transformation. Primary TiC grows in dendritic shape due to the formation of composition undercooling. Binary eutectic TiC grows in equiaxed or near-equiaxed shape. A small quantity of TiC may form twin structure during nucleation and growth. The twin plane is (111) plane.