自生TiCp/Ti复合材料中TiC的生长习性

利用配位多面体生长基元理论研究了自生TiCp/Ti复合材料中TiC的生长习性。TiC晶体的配位多面体生长基元为TiC6。生长基元进入{100}面时为4个棱边同时联结，生长速率最快，不易显露；进入{111}面时为共面联结，生长速率最慢，容易显露。因此，TiC晶体的理想形态为{111} 面为显露面的八面体。TiC晶胚在熔体中生长时，受传热传质过程的影响，6个顶角所处的{100}方向生长速率加快，形态失稳，从{100}方向顶角部位生长出二次枝晶臂，最终形成棱面枝晶状TiC。如枝晶形成时低生长速度的晶面上形成大量的晶体缺陷，则它们的生长速度加快，棱面消失，成为光滑枝晶。

STUDY OF GROWTH HABIT OF TiC IN TiCp/Ti COMPOSITES

Growth habit of TiC in TiCp/Ti composites fabricated using melting cast process was investigated by means of coordination polyhedron growth unit theory. The growth unit of coordination polyhedron for fcc structure TiC crystal is TiCe- Growth units stack on the {100} planes with the linking mode of edges, which leads to the {100} planes have fastest growth rate and be non-present face. On the {111} planes, the growth units linked with the mode of faces contributing to the {111} planes have slowest growth rate and become present face. Thus, TiC crystal is octahedral geometry and the {111} planes are its present face. During non-equilibrium solidification of TiCp/Ti composites, secondary deridrite arms are formed along {100} directions of TiC crystal having fastest growth rate and on the planes having slower growth rate, crystal defects such as screw dislocation are formed owing to higher cooling rate that makes TiC crystal lose facet characteristic. On the condition of directional solidification, the cooling rate is slow and crystal face of TiC remains facet characteristic resulting in prism dendrites.