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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 12    No. 6    December 2002

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Formation and growth mechanism of TiC crystal in TiCp/Ti composites
JIN Yun-xue(金云学), WANG Hong-wei(王宏伟),
ZENG Song-yan(曾松岩), ZHANG Er-lin(张二林)

National Key Laboratory for Precision Hot Processing of Metal, Harbin Institute of Technology, Harbin 150001, China

Abstract:Ti-C and Ti-Al-C alloys were prepared using gravity and directional solidification processes. Morphologies of TiC crystal were investigated by using SEM, XRD and EDX. Also, the formation and growth mechanism of TiC crystal have been analyzed on the basis of coordination polyhedron growth unit theory. During solidification of titanium alloys, the coordination polyhedron growth unit is TiC6. TiC6 growth units stack in a linking mode of edge to edge and form octahedral TiC crystal with {111} planes as present faces. Although the growing geometry of TiC crystal is decided by its lattice structure, the final morphology of TiC crystal depends on the effects of its growth environment. In solute concentration distribution, the super-saturation of C or TiC6 at the corners of octahedral TiC crystal is much higher than that of edges and faces of octahedral TiC crystal. At these corners the driving force for crystal growth is greater and the interface is instable which contribute to quick stacking rate of growth units at these corners and result in secondary dendrite arms along TiC crystallographic 〈100〉 directions. TiC crystal finally grows to be dendrites.

 

Key words:   titanium alloys; composites; TiC; morphology; growth mechanism

ISSN 1672-7029
CN 43-1423/U

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