Formation mechanism of the porous zone at the bonded Si3N4/Ni interface

Diffusion bonding of Si3N4ceramic to itself was performed using Ni interlayer.Aflat Si3N4/Ni interface was found at a lower temperature(1 273 K).Whereas at a higher temperature(1 473 K),a porous zone located at the Si3N4/Ni interface and some petal-like Ni3Si compounds precipitated in the Ni interlayer were observed.The formation mechanism of the porous zone was investigated based on a fracture analysis.An additional stress(σadd) generated at the Si3N4/Ni interface played an important role in the formation of the porous zone,which was resulted from the aggregation of nitrogen during the bonding process.A calculation equation of the σaddwas derived to analyze its effects.The results indicated that σaddwas directly in dependent with diffusion bonding temperature and dwell time.