SURFACE STRUCTURE AND GROWTH MECHANISM OF TiB₂ PLATE IN TiAl-B ALLOYS

Ti-54Al-xB alloys have been produced by an in-situ method. The microstructure and phases constituent of these alloys were investigated by XRD and SEM. The results show that there are needle shape dendrites which are parallel to 0001 on the edge of TiB₂ plate and convex flakes which are perpendicular to 0001on the surface of TiB₂ plate. These needles or flakes exhibit facets parallel to those of TiB₂ plate. It was analyzed that the Al rich layer and inhomogeneity in supersaturation at the solid-liquid interface resulting from non-equilibrium solidification may make the solid-liquid interface unstable, and lead TiB₂ plate to forming the surface structure.