Interfacial evolution and toughening mechanisms in diffusion-bonded Nb/Nb₅Si₃ laminated composites

Laminated Nb/Nb₅Si₃ composites were fabricated via diffusion bonding to investigate interfacial evolution and its impact on mechanical properties. The effects of bonding pressure and holding time on interfacial microstructure and fracture behavior were systematically studied. Increasing the bonding pressure from 20 MPa to 50 MPa improved atomic interdiffusion, eliminated voids, and raised the bonded ratio from 74.4 % to 96.4 %. Prolonged holding time promoted the removal of the NbSi₂ phase and the formation of a continuous Nb₅Si₃ layer, contributing to a more ideal laminated structure. Mechanical testing demonstrated that enhanced interfacial integrity led to improvements in tensile strength (450 MPa), bending strength (1040 MPa), and fracture toughness (21.94 MPa·m^1/2) under optimal conditions (1170°C, 50 MPa, 4 h). Fracture analysis revealed a mixed ductile–cleavage mode dominated by interlaminar failure. Two main bending fracture behaviors were observed: interlayer delamination and translaminar crack growth. The improved toughness was attributed to extrinsic toughening through crack deflection along interfaces and intrinsic toughening via crack blunting within the Nb₅Si₃ layer. This study highlights the key role of interfacial phase control in achieving damage-tolerant, high-performance laminated composites and provides guidance for the design of high-temperature structural intermetallic systems.