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

Highlights: •Using zwitterionic surfactant to enhance the dispersion of the CNTs on the powder surface. •CNTs as carbon source decreased the formation temperature of Ti2AlC. •Al2O3 was generated in situ from the oxygen atoms introduced in the drying procedure. •Nanosized Ti3Al was precipitated at 1250 °C and distribute in the TiAl matrix homogeneously. •Ti2AlC–Al2O3/TiAl composite was synthesized in situ by sintering pre-alloy Ti–Al coated with CNTs. -- Abstract: 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