Interfacial microstructure and properties of Si₃N₄/Ni/TiAl joint boned by diffusion-bonding

Diffusion bonding of Si₃N₄ ceramic and TiAl alloy was achieved using 80μm thick Ni foil as interlayer.The interfacial microstructure was TiAl/Al₅Ni₂Ti₃/AlNi₂Ti/Ni₃(Ti,Al)/Ni(s,s)+Ni₃Si/Si₃N₄,which was analyzed by SEM,EDS and XRD.The effect of bonding temperature on interfacial microstructure and joining properties of the Si₃N₄/Ni/TiAl joints were investigated in details.With an increase of temperature,the inter-diffusion rate of alloying elements at the TiAl/Ni and Ni/Si₃N₄ interfaces increased gradually,which led to an increase in thickness of reaction layers.A porous zone formed between Ni and Si₃N₄ when the temperature was relatively high,where cracks performed to come forth.The highest shear strength of 104.2 MPa was obtained when the specimen was bonded at 1 000℃ for 2 h.Fracture analysis indicated that cracks initiated at the Si₃N₄/Ni interface and propagated to Si₃N₄ substrate finally ruptured within ceramic.