Influence of Al content on constitutes and morphologies of borides in Ti-Al-B alloys

Boride particles reinforced titanium alloy matrix composites were prepared by the melting-casting method. The phase constitutes and morphologies of borides varying with the Al content were investigated by XRD and SEM techniques. The results indicate that the phase constitutes of composites are influenced by the Al content. At lower Al content, the matrix is α-Ti, the boride is simply TiB. When the Al content is increased, α₂ and γ phases are formed in the matrix and the TiB₂ phase appears in the boride instead of TiB. Finally, the total content of β appears in the form of TiB₂. The eutectic TiB particles are needle-like or in the form of plates with a size of 20-50μm. TiB may have a grain-boundary character of distribution when the amount of TiB is less. With the increasing of B content, the lath-like TiB appears and the typical form of TiB₂ is hexagonal prism with block-shape or branches.