Fabrication, microstructure characterization and fracture behavior of a unique micro-laminated TiB-TiAl composites

A feasible manufacturing & forming integration technology for production of TiB-TiAl composite sheets was successfully explored by employing reaction annealing of sandwich-structured (TiB/Ti)–Al laminates. Phase transformation, microstructure evolution of (TiB/Ti)–Al laminates during different reaction annealing processes were systematically investigated by means of optical microscope, scanning electron microscopy, transmission electron microscope and X-ray diffraction. The results showed that the resulting TiB-TiAl composites displayed a unique micro-laminated structure, composing of alternating fully lamellar (α₂-Ti₃Al/γ-TiAl) layers, equiaxed γ-TiAl layers and TiB-rich layers. Actually, TiB whiskers exhibited a layered distribution in fully lamellar α₂/γ layers, which was in favor of α₂/γ lamellae refinement. Moreover, formation mechanism of the micro-laminated structure was illustrated. It is noteworthy that the micro-laminated TiB-TiAl composites showed a significant increase in ductility while maintaining or even improving high-temperature tensile strength, in comparison with monolithic TiAl. In addition, fracture behavior of the novel TiB-TiAl composites was characterized by three-dimensional X-ray microscope (3D-XRM) and finally strengthening-toughening mechanism were clarified.