Synthesis and Fracture Characteristics of TiB2-TiAl Composites with a Unique Microlaminated Architecture

Microstructural evolution of as-rolled (TiB2/Al)-Ti laminates in the process of multistep heat treatments and microstructural characteristics of the resulting TiB2-TiAl composites were investigated in detail by scanning electron microscope (SEM) and transmission electron microscope. The desired TiB2-TiAl composites exhibited a unique microlaminated structure consisting of alternating fully lamellar alpha(2)-Ti3Al/gamma-TiAl layers and TiB2-rich layers. Moreover, the formation mechanism of the microlaminated structure was elucidated. It is noteworthy that the TiB2-TiAl composites showed improved high-temperature tensile properties and room-temperature fracture toughness due to the strengthening effect of TiB2 particles and the structure effect of the unique microlaminated microstructure. In addition, the fracture behavior of the microlaminated TiB2-TiAl composites during the dynamic tensile was characterized by combining use of the three-dimensional X-ray microscope (3D-XRM) and SEM. The results indicated that pores and cracks preferred to initiate in the brittle TiB2-rich layer and showed a typical layered distribution, and then expanded into a nearby fully lamellar alpha(2)/gamma layer and kept propagating through the entire alpha(2)/gamma layer into another TiB2-rich layer, repeatedly, and finally the main crack propagated through all the fully lamellar alpha(2)/gamma layers and TiB2-rich layers, eventually resulting in failure. Thus, the fracture mechanism of the innovative microlaminated TiB2-TiAl composites was proposed.