Temperature-dependent reversed fracture behavior of multilayered TiBw/Ti–Ti(Al) composites

Abstract

Engineering strong and ductile structural materials has been an enduring pursuit over the past few decades. Here we proposed a heterogeneous laminated/gradient integrated strategy with the purpose of maximizing the role of laminated or gradient structure for performance enhancement. Such a heterogeneous TiBw/Ti–Ti(Al) composite is structurally characterized by a layered distribution of TiB whisker and a compositional gradient with depth, and fabricated by a simple diffusion annealing of alternately stacked TiBw/Ti and Al foils. The mechanical properties were evaluated at room and high temperatures, and the mechanism behind superior strength-ductility synergy was analyzed by post-mortem characterization of deformation physics and quantitative crack statistics. Our results demonstrated that the major stress-bearing constituents gradually changes from Ti(Al) to TiBw/Ti layers as the deformation temperature increases, leading to the temperature-dependent reversed fracture behavior. The contribution of sub-critical cracks is in particular discussed, and the key viewpoint we proposed is that the larger the crack density, the wider the crack distribution, the better the mechanical performance, as long as the sub-critical crack is still in its “stable” domain and does not develop into unstably critical major crack causing catastrophic fracture.