In situ synthesis of Ti2AlC-Al2O3/TiAl composite by vacuum sintering mechanically alloyed TiAl powder coated with CNTs

Bulk Ti2AlC-Al2O3/TiAl composites were in situ synthesized by vacuum sintering mechanically alloyed Ti-50 at.% Al powders coated with carbon nanotubes (CNTs). The pre-alloyed Ti-50 at.% Al powder was obtained by ball milling Ti and Al powders. The multi-walled carbon nanotubes as the carbon resource were covered on the surface of the pre-alloyed powders by immersing them into a water solution containing the CNTs. A zwitterionic surfactant was used to enhance the dispersion of the CNTs on the powder surface. The samples were cold pressed and sintered in vacuum at temperatures from 950 to 1250 °C, respectively. The results show that the reaction of forming Ti2AlC can be achieved below 950 °C, which is 150 °C lower than in the Ti-Al-TiC system and 250 °C lower than for the Ti-Al-C system due to the addition of CNTs. Additionally, the reinforcement of Al2O3 particles was introduced in situ in Ti2AlC/TiAl by the drying process and subsequent sintering of the composite powders. Dense Ti2AlC-Al2O3/TiAl composites were obtained by sintering at 1250 °C and exhibited a homogeneous distribution of Ti2AlC, Al2O3 and precipitated Ti3Al particles and a resulting high hardness.