Architecture design and significant toughness enhancement of Ti6Al4V based composites with gradient laminate distributed TiB

Titanium Matrix Composites (TMCs) are well-known for their high specific strength and elastic modulus, however short of toughness. In the present work, in order to achieve better toughness, TiB/Ti6Al4V composites with a novel multiscale gradient-laminate network structure were fabricated via powder metallurgy method combining powder stacking process. The composites exhibit a laminated structure with gradient volume fraction of TiB on the macroscopic scale and a network structure of TiB distribution on the microscopic scale. Three-point bending tests were carried out to reveal the mechanical properties of the composites. The bending strength and fracture strain achieve 1950 MPa and 0.097 in the gradient-laminated composites, which were improved significantly compared to those in the monolithic composites. The bending toughness (148.3 × 103 kJ·m-3, represented by work of fracture during the three-point bending test) of the gradient-laminated composites is about 70% higher than that of the composites without laminated architecture. Fractography suggests that the crack deflection and prolonged crack propagation path contribute to the increase of fracture strain. The crack blunting, network microcracks and interface cracks are also beneficial to improving the bending strength and toughness.