Microstructure And Mechanical Properties Of Si₃N₄ Ceramics Joints With β-SIALON-GLASS Interlayer

Commercial Si₃N₄ ceramics were joined usingβ-sialon-glass adhesives, effects of joining parameters, adhesive composition on the microstructure and mechanical properties of the joints were analyzed by means of SEM, EDS, DTA and XRD. Before joining the Si₃N₄ ceramics, the wettability ofβ-sialon-glasses adhesives on Si₃N₄ substrates was investigated.The DTA analysis of the ofβ-sialon-glass reveals that reaction temperature of adhesives was 1250℃, and theα-Si₃N₄ begin to dissolve when it was heated to 1440℃. According to the wetting results, it can be concluded that only adhesives with low content ofβ-sialon can spread on the surface of Si₃N₄ matrix and the contact angle between the adhesives and Si₃N₄ increases with the content ofβ-sialon. A few elongatedβ-sialon grains precipitated in the spreading layer and the amount of the producedβ-sialon grains increases with the designed content. There exists a diffusion layer (about 20-50μm) beside the interface, which decreases in thickness with increasing the designedβ-sialon content.The Si₃N₄ joints consist ofβ-sialon-glass interlayer, Si₃N₄ matrix and diffusion layer close to the interface. With the joining temperature increasing, the rate of diffusion and reaction increase and the thickness of welding seam decreases. The strength of the joint decreases with the temperature rising using 15β′adhesive, but it increases for 60β′adhesive. For 30β′and 45β′adhesive, the strength reaches the maximum value at 1600°C holding for 30min. The influence of holding time on the strenght is similar to that of temperature.At a joining temperature of 1600°C holding for 30 min, the 45β′adhesive was converted to an composite ofβ-sialon-glass ceramic, with which a maximum joining strength (239MPa) can be obtained. Fracture analysis shows that the fracture crack emerge at the the Si₃N₄ matrix, then pass through the joint. The maximum strength of the joint using Si5.4Al0.6O0.6N7.4-Y_1.75Si_2.625Al₁₀O_7.5N_1.25 adhesive is only 74.7 MPa.