Interfacial microstructure and properties of TiAl joints brazed with composite filler reinforced by particles

Interfacial microstructure and properties of TiAl joints brazed with composite filler reinforced by particlesTiAl alloy was brazed with AgCuTiC composite filler metal reinforced by nano-Si₃N₄ particles.The typical interfacial microstructures in TiAl/AgCuTiC/TiAl joint are TiAl/Al- Cu₂Ti/Ag_(s,s)+TiN+Al₄Cu₉+Ti₅Si₃,which are analyzed by SEM,EDS and XRD.Investigation results indicate that the active element Ti dissolves from TiAl substrate and reacts with nano-Si₃N₄ to form fine compounds including TiN,Ti₅Si₃ and Al₄Cu₉ during brazing process.These compounds are uniformly distributed in Ag solid solution,which lead to the formation of Ag based composite in brazed seam.The desired microstructure can not only strengthen the brazed seam,but also reduce the residual stresses in joints by decreasing the mismatch of coefficient of thermal expansion between TiAl substrate and brazing seam, which greatly improves the joint properties.The maximum shear strength of 278 MPa can be obtained with AgCuTiC composite filler with 3% nano-Si₃N₄ addition at 880℃ for 5 min,which is 40% higher than that brazed joint using AgCuTi directly.