Effect of processing parameters on the microstructure and mechanical properties of TiAl/Ti₂AlNb laminated composites

In order to improve the intrinsic brittleness of TiAl alloys, Ti₂AlNb alloys with outstanding ductility and toughness at room temperature, and good high-temperature performance are competitive candidates in constructing the TiAl-based laminated composites. In this work, TiAl/Ti₂AlNb laminated composites are successfully synthesized by vacuum hot pressing combined with the foil-foil (sheet) metallurgy. Under the pressure of 65 MPa, different holding time and temperature of hot pressing are tried and the optimized fabrication parameter is acquired as 1050 °C/120 min/65 MPa. Along with the changes of processing parameters, the defect, microstructure, interface, phase transformation and the corresponding mechanical properties are detailly discussed. The results show that the TiAl/Ti₂AlNb laminated composite fabricated at 1050 °C for 2 h achieves a good metallurgical interface bonding. The corresponding interface microstructure is composed of region I and region II. The region I consists of O, α₂ and B2/β phase, and region II is made up of α₂. Subsequently, the tensile tests indicate that the composite synthesized at 1050 °C for 2 h possesses a maximum strength of 812 MPa and a total elongation of 1.31% at room temperature, and a strength of 539.71 MPa and the highest total elongation of 10.34% at 750 °C. The well synergistic deformation ability between the interface and the two base alloys endows the composite an excellent tensile performance. Moreover, the composite processed at 1050 °C for 2 h behaves the best fracture toughness in both arrester orientation and divider orientation with the value of 32.6 MPa.m^1/2 and 30.1 MPa.m^1/2, respectively. The Ti₂AlNb alloy in the laminated structure effectively release the stress around the crack tip and plays a role in toughening. Further, crack deflection, crack bridging, crack blunting and fragmentation also make contributions to enhance the fracture toughness of the laminated composites.