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 phase 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 [0001] on the surface of TiB₂ plate. These needles or flakes exhibit facets parallel to those of TiB₂ plate. It is shown through analysis that the Al rich layer and the supersaturation inhomogeneity at the solid-liquid interface resulting from non-equilibrium solidification may make the solid-liquid interface unstable and lead TiB₂ plate to form such a surface structure.