Effects Of Diffusion Bonding Conditions On Microstructures And Mechanical Properties Of SiC/SiC Joints

The diffusion bonding process was used to connect Silicon carbon(SiC)ceramics. The effects of composition(Ti, Ni, Ti/Ni/Ti, Ti-dipping, Ti-preforming)and joining parameters(temperature, pressure, holding time) on microstructures andmechanical properties of SiC/SiC joints was studied by using X-rayDiffraction(XRD), Scanning Electron Microscope(SEM), Energy DispersiveSpectrometer(EDS) technology and shear strength test.The results show that the microstructures and mechanical properties of SiC/SiCjoints using Ti foil, Ti/Ni/Ti foil as the intermediate layer were better when joiningtemperature, pressure, and holding time were1400℃,30MPa,1h. Specificperformance: the main phases of the weld joints were TiC and Ti5Si3, Ni-Si; thewidth of weld joints were38μm and45μm, and the C, Si element of Silicon carbonceramics diffusion in the intermediate layer; the shear strength of SiC/SiC jointswas68.9MPa and138.0MPa, the tissue of fracture surface was dense; the hardnessof SiC/SiC joints weld was13.7GPa and19.0GPa, elastic modulus was301.4GPaand352.1GPa. In the meantime, using Ti/Ni/Ti foil as the intermediate layer, thedensity of weld joints’ microstructures and bonding strength were better than Ti foilgroup. The disciplines were same as the joining parameters transformed.The effects of joining parameters on SiC/SiC joints performance were studied,using Ti/Ni/Ti foil as the intermediate layer were much better. Specific performance:the SiC/SiC joints’ structure compactness and mechanical properties were muchbetter with the increase of temperature, to achieve the best at1600℃, the width ofweld joints, shear strength, the hardness of joints weld, the elastic modulus of jointsweld were13μm,207.6MPa,24.7GPa,547.3GPa; the SiC/SiC joints’ structurescompactness and mechanical properties were also much better with the increase ofpressure, to achieve the best under the pressure of45MPa, the width of weld joints,shear strength, the hardness of joints weld, the elastic modulus of joints weld were13μm,189.2MPa,21.2GPa,465.8GPa; but with the holding time prolonging, theperformance of the SiC/SiC joints’ structures compactness and mechanicalproperties showed the trend.of decrease.The study also found that the connection temperature was the most importantfactor of affecting the SiC/SiC joints’ properties relative to the pressure and holdingtime. The highest bonding strength of SiC/SiC joints using Ti/Ni/Ti foil as the intermediate layer was found when connecting temperature, pressure and holdingtime were1600℃,30MPa,1h.