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 similar to 800 degrees 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 degrees 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/mm(3), an almost completely dense reinforcement skeleton (similar to 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 Othick/thin lath-like phase and O (short rod-like) phase. L-II is mainly composed of B-2/beta phase, acicular alpha(2) phase and nanoscale omega-Ti3NbAl2 phase. The L-III mainly consists of B-2/beta phase. The L-IV is composed of alpha(2) phase. The deformability of each phase in the composite: B-2/beta phase > O phase > gamma phase > alpha(2) phase >omega 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.