激光原位制备TiB/Ti-6Al-4V复合涂层中TiB管状结构的形成机制

利用透射电镜(TEM)、电子背散射衍射(EBSD)技术,系统观察、分析了激光原位制备TiB/Ti-6Al-4V复合涂层中TiB生长形态、分布以及晶体学取向,以探讨管状结构TiB的形成机制。结果表明:涂层中TiB的形态主要有棒状和针状2种,受控于生长时间和元素浓度2个因素。棒状TiB形核于过共晶成分区域,针状TiB形核于共晶成分和亚共晶成分区域。当TiB的直径和生长速度之积超过临界值时,(010)_(B27)和(001)_(Bf)晶面的生长将不再稳定。界面边缘区域更易获得硼原子,生长速度快于中心区域,而边缘区域对硼元素的消耗进一步抑制了中心区域的生长,从而产生了管状结构。随着TiB直径的增加,管状结构出现的概率增加。

Formation mechanism of the tubular TiB in situ formed in TiB/Ti-6Al-4V composite coating by laser cladding.

The morphology, distribution and crystallographic orientation of TiB in situ formed in TiB/Ti-6Al-4V composite coating by laser was observed and analyzed by TEM, EBSD systematically, in order to explore the formation mechanism of tubular TiB. The results show that, TiB showed two morphologies: rod and needle. And the morphology of TiB crystals is controlled by growth time and element concentration. Rod-like TiB nucleated in the hypereutectic region, and needle-like TiB nucleated in the eutectic and hypoeutectic region. The growth of (010)_B27 and (001)_BF planes will no longer be stable, when the the product of diameter and the growth rate of TiB exceed the critical value. The growth rate in the edge region of TiB is faster than the center due to the concentration of B. TiB eventually forms a tubular structure because B element is consumed by the growth of edges that further inhibits the growth of the central region.With the increase of diameter of TiB, the tubular structure appears more frequently.