Interfacial reaction and joint strength of silicon nitride ceramic composites bonded with Y 2O 3–Al 2O 3–SiO 2–Si 3N 4 mixture

Abstract

Silicon nitride ceramic composite was joined to itself by heating an interlayer of Y 2O 3–Al 2O 3–SiO 2–Si 3N 4 mixtures above their liquid temperatures in flowing nitrogen. The microstructure and chemistry of joints were characterized by scanning electron microscopy, electron probe microanalyses and X-ray diffraction, respectively. The results show that some elements of adhesive (Y, Al, O) diffuse into silicon nitride ceramic composite to form a diffusion layer. At 1600 °C, the content of Si 2N 2O and β-Si 3N 4 increases with an increase in holding time. When the bonding temperature is higher than 1600 °C, the content of β-Si 3N 4 increases. The joining strength of the joint depends on the interfacial reaction, and a maximum joining strength of 350 MPa measured by the four-point bending test is achieved for the Si 3N 4 composite–Si 3N 4 composite joint bonded at 1600 °C for 10 min. The destructed part is considered to start at the diffusion layer, indicating that the joining strength will be much higher than that value.