Surface morphology and growth mechanism of primary TiB₂ in TiAl-B alloys

Ti-54Al-xB alloys have been produced by an in-situ method. The microstructure and the phase institute of these alloys were investigated by XRD and SEM. The results show that there are pyramidal protrusions or rod shape dendrites on (0001) facets and some very thin convex flakes on {10 10̄} facets of primary TiB₂. The facets of these protrusions or rods and thin convex flakes are parallel to the facets of primary TiB₂. The thickness and the height of these flakes are smaller than 0.2 °m and 1.5 °m, respectively. Some of the flakes are so developed that they exhibit the ring shape layer upon layer surrounding primary TiB₂. The Al rich layer and the inhomogeneity in supersaturation at the solid-liquid interface resulting from the non-equilibrium solidification may make the solid-liquid interface instable, and lead the primary TiB₂ surface to engender rod shape dendrites on (0001) planes or very thin convex flakes on {10 10̄} planes.