Microstructure and properties of Si₃N₄ joints joined with RE-Si-Al-O-N (RE=Y or Lu) glass

Si₃N₄ ceramics were joined with a Si₃N₄-Al₂O₃-RE₂O₃-SiO₂ (RE=Y or Lu) powder mixture via in-situ formed RE-Si-Al oxynitride glass interlayer. The effects of bonding temperature, holding time and rare-earth element type on the microstructure and properties of the joints were investigated. The oxidation behavior of the joints was analyzed. The densification and uniformity of the seam as well as the diffusion between Y-Si-Al-O-N glass as a solder and Si₃N₄ matrix are improved when the holding time is increased. The bonding strength of the joints is 218 MPa when the joints were hold at 1550 ℃ for 30 min. Moreover, the strength of the joints after oxidation at 1200 ℃ for 20 h is still 82% of the strength at room temperature., The increase of temperature can favor the densification of the seam and precipitation of more β-sialon phase in the seam when Lu-Si-Al oxynitride glass is used. The bonding strength of the joints increases with the bonding temperature.