Composition and morphology of diborides in Al-Ti-B alloys after annealing at 1873 K

摘要

In the investigation, Al-Ti-B alloys with different Ti/B ratios were annealed at 1873 K for 10 hours. Under this condition diboride particles were in contact with molten aluminium. During annealing considerable growth of remaining unmelted diboride particles took place. The composition of diboride particles shifted extremely close to the composition of pure TiB_2 regardless of the Ti/B ratios in the alloys, indicating that in equilibrium almost pure TiB_2 coexisted with a melt. Diboride particles were bound with well-defined crystal facets. Types and relative size of the facets depended on the Ti/B ratio. It is strongly indicated that an excess of Ti (B) in the melt over that needed to form TiB_2 stabilizes crystal planes having planar arrangement of Ti (B) atoms.