Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti₂AlNb/TiAl matrix composite with a crossed-lamellar structure

TiAl alloys with low density, high creep resistance and high temperature performance are considered as candidate materials to replace nickel-based superalloys in the range of 700∼800 °C. However, the intrinsic brittleness of TiAl alloys has always been the biggest bottleneck restricting their development. In this paper, a bioinspired interpenetrating Ti₂AlNb/TiAl composite with crossed-lamellar structure was prepared by combining selective laser melting (SLM) and vacuum hot press sintering (HPS) under the condition of 1150 °C/1 h/45 MPa, to improve the strength and toughness of the composite. Meanwhile, the metallurgical defects and microstructure of Ti₂AlNb reinforcement skeleton printed under different volume energy densities (VEDs) were investigated, as well as the evolution of the microstructure at the interface region of the composite was systematically studied. What's more, we studied the mechanical properties of the composite including nanoindentation test, room temperature tensile and bending tests. The results show that the VED is 88.89 J/mm³, an almost completely dense reinforcement skeleton (∼99.8 %) is obtained. The interface region can be divided into four different reaction layers, namely L_Ⅰ, L_Ⅱ, L_Ⅲ and L_Ⅳ, due to the diffusion of elements. L_Ⅰ is mainly composed of O_{thick/thin lath-like} phase and O _{short rod-like} phase. L_Ⅱ is mainly composed of B₂/β phase, acicular α₂ phase and nanoscale ω-Ti₃NbAl₂ phase. The L_Ⅲ mainly consists of B₂/β phase. The L_Ⅳ is composed of α₂ phase. The deformability of each phase in the composite: B₂/β phase > O phase >γ phase >α₂ phase >ω phase. The tensile strength and fracture toughness of bioinspired interpenetrating Ti₂AlNb/TiAl matrix composite are increased by 24.0 % and 89.0 %, respectively, compared with TiAl alloy, which is mainly contributed to the strong interfacial bonding between matrix and reinforcement as well as the synergistic effect of Ti₂AlNb reinforcement with high strength and toughness.