Formation of heterogeneous interfaces in the TiAl/Ti2 AlNb layered composite and its effect on the fracture toughness

TiAl/Ti2 AlNb intermetallic-intermetallic laminated (IIL) composites featuring brittle/ductile heterogeneous interfaces were fabricated through vacuum hot-pack rolling. The microstructures and the phase transformation behaviors of the interfaces of the IIL composites before and after annealing at 900 degrees C/6 h were investigated. The heterogeneous interfaces are composed of four distinct regions, individually I ( beta o + gamma + alpha 2 ), II ( beta o /B2 + omega) (brittle part), III (O lath), and IV (equiaxed O) (ductile part) regions from TiAl to Ti2 AlNb side. Notably, after annealing, an equiaxed O band approximately 50 mu m wide was observed in region IV of the interface. In addition, a significant microhardness variation was observed between regions II and IV of the interface, where region II exhibited higher hardness compared to the TiAl alloy, and region IV displayed lower hardness than the Ti2 AlNb alloy. The enhanced fracture toughness of the IIL composites, three times that of the TiAl base alloy, is attributed to the formation of the brittle/ductile heterogeneous interfaces and the layered design incorporating the Ti2 AlNb alloy. The corresponding toughening mechanism was further discussed. The brittle II region plays a role in increasing crack branching, while the ductile IV region inhibits the propagation of microcracks and prevents the formation of main cracks. This work highlights the crucial role of the brittle/ductile heterogeneous interface in the toughening of laminated composites. Furthermore, the discovery of the O band provides novel insights into the design of TiAl/Ti2 AlNb heterostructures. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.