Investigations of interfacial reaction and toughening mechanisms of Ta fiber-reinforced TiAl-matrix composites

Continuous fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. Ta fiber with outstanding plasticity and toughness is regarded as a promising reinforcement. In this work, a 10 vol% Ta fiber-reinforced TiAl composite was prepared by combining slurry casting and vacuum hot pressing under condition of 1150 °C/ 35 MPa/ 2 h. Microstructure of interfacial reaction zone of the composite was investigated; meanwhile, thermodynamic calculation and theoretical analysis were conducted to explain the formation mechanisms of the reaction products. Three types of reaction products σ-Ta2Al, B2 and α2 phases were formed between Ta fiber and TiAl matrix. σ phase was adjacent to Ta fiber with a fine grain structure, which was formed due to the lowest formation free energy. The aggregation of β stabilizers in Ti-rich region resulted in the formation of B2 phase that was close to σ phase. α2 phase relied on B2 phase to nucleate and grow based on the Burgers relationship and their structure symmetry. Three-point bending tests show the fracture toughness (KIC) of the Taf/TiAl composite was 58% higher than that of pure TiAl matrix. The main toughening mechanism of the Taf/TiAl composite was plastic deformation of the Ta fiber, meanwhile the interfacial debonding also had a contribution to toughening the TiAl alloy. The interfacial debonding location was mainly at the Ta / LI-σ interface due to the existence of thermal residual stress.