The Mechanism Of Changing And Control Of Morphology Of TiC In TiC/Ti6Al4V Composites

TiC particles reinforced Ti6Al4V matrix composites were fabricated by using in-situ melting-casting process.The changing of morphology of TiC with the variety of C content and the effects of trace B or Zr element on morphology of TiC in TiC/Ti6Al4V composites were investigated by means of SEM,XRD and EDS.The macrohardness of the TiC/Ti6Al4V composites were measured by using a macrohardness tester.The observation results of morphology of TiC in as-cast TiC/Ti6Al4V composites show that the morphology of TiC in as-cast TiC/Ti6Al4V composites varies with the changing of C content.When the carbon content is 0.15wt.%,TiC is of featheriness or granular.When the carbon content exceeds 0.2wt.%,TiC is mainly of chain-type TiC which consists of featheriness and wheat-shape TiC. And the TiC is mainly of short-bar shape TiC when C content is near the eutectic point.When C content increases further,the exiguous dendritic shape TiC appears and with the increasing of C content,the dendritic TiC becomes more developed. Simultaneously,the hardness of the composites increases.When C content is 2wt.%in TiC/Ti6Al4V composites,the addition of trace B can refine TiC dendrite.The average grain size of TiC dendrite is decreased gradually with the increasing content of B from 0.01wt.%to 0.04wt.%and even short-bar shape and particle TiC appear.With the increasing of B content,the hardness of the composites also increases.When B content is 0.1wt.%,the fibre-shape TiB appears and with the increasing of B content,the quantity and size of TiB increases gradually,but the morphology and distribution of the dendritic shape TiC have no variety obviously.The investigated results of the effects of Zr element addition on morphology of TiC in TiC/Ti6Al4V composites containing 2wt.%C indicate that when Zr content is 1wt.%-4wt.%,the morphology of the primary TiC is dendrite.And the petal-shape,piece-shape or palpus-shape eutectic TiC containing Zr separates out around the primary TiC.With the increasing of Zr content,the primary TiC becomes finer and the eutectic TiC increases.When Zr content continues to increase,the effects of Zr element on morphology of the primary TiC weakens and the primary TiC becomes coarse.With the increasing of Zr content,the hardness of the composites increases.The mechanism of changing of morphology of TiC with the variety of C,B or Zr content in TiC/Ti6Al4V composites were also investigated in this paper.The obtained results could be available for reference in controlling nucleation and growth of TiC and improving performance and stability of TiC reinforced titanium alloy matrix composites.