Microstructure and mechanical properties of multi-phase TiAl alloy matrix composites consolidated via field-assisted sintering technique

In this study, fully densified Si₃N₄/TiAl composites were fabricated using the field-assisted sintering technique (FAST). Microstructural analysis showed the evolution of a continuous network structure consisting of minor fractions of in-situ formed Ti₂AlN, unreacted Si₃N₄ ceramic particles and dominant Ti₅Si₃ intermetallic phases within the TiAl matrix at Si₃N₄ content above 1.5 wt%. The hardness of the developed composites increases with increasing Si₃N₄ content, with 7Si₃N₄/TiAl composite exhibiting the highest hardness of approximately 487 HV_1.0, which was about 57% higher than that of the sintered pure TiAl alloy. Among the sintered samples, 1.5Si₃N₄/TiAl composite displayed the highest flexural strength of 832.65 ± 12.88 MPa (34.3% higher than pure TiAl matrix) with a deflection of 0.14 mm. In contrast, the lowest flexural strength and deflection of 535.44 ± 21.14 MPa and 0.09 mm were obtained in composite reinforced with 7 wt% Si₃N₄ ceramic content. The fractured surface of the sintered samples displayed predominantly cleavage fracture mode.