Microstructure and properties of new type Ti₃AlC₂-Al₂O₃/TiAl₃ composites

The TiAl₃ matrix intermetallic composites reinforced by in-situ synthesized two phases of Ti₃AlC₂ and Al₂O₃ were produced by mechanically ball-milled and hot pressing of Al-TiO₂-TiC system. The reaction mechanism, microstructure, mechanical properties and oxidation-resistance properties of the composites were investigated using DSC, XRD, SEM and TEM. The results indicate that dense Ti₃AlC₂-Al₂O₃/TiAl₃ composites with homogeneous and pyknotic microstructure can be obtained by sintering 50 h ball-milled power mixture at 1 250 ℃/50 MPa for 10 min. The density, Vickers hardness, three-point bending strength, fracture toughness and compressive strength at room temperature of Ti₃AlC₂-Al₂O₃/TiAl₃ composites reach 3.8 g/cm³, 8.4 GPa, 658.9 MPa, 7.9 MPa·m^1/2 and 1 742.0 MPa, respectively, and the elevated-temperature compressive strength at 1 000 ℃ reaches 604.1 MPa. The toughening mechanism of Ti₃AlC₂-Al₂O₃/TiAl₃ composites is primarily attributed to the pull-out of Ti₃AlC₂ and Al₂O₃ particles, crack deflection and crack bridging by Ti₃AlC₂ phase, and the deformation and delamination of Ti₃AlC₂ particles. Tough the oxidation scales generated in the temperature range from 700 to 1 000 ℃ are not dense, the Ti₃AlC₂-Al₂O₃/TiAl₃ composites still exhibit excellent cyclic oxidation resistance.