Research On Process And Mechanism Of Al₂O₃-B₂O₃-SiO₂ Micro Crystalline Glass Connecting Al₂O₃/ZTA Ceramics

Al₂O₃ ceramics and ZTA ceramics have high mechanical strength, resistance to acid and corrosion, and high temperature resistance, are widely used in various industries. However, it is difficult to be processed into complex structure and large size components because of poor machinability, so it’s important to form reliable connection. There are many problems when using the brazing and diffusion welding method to join ceramics, such as the large residual stress in joints, and poor chemical stability. The project propose a new method to join ceramics with Al₂O₃-B₂O₃-Si O₂（ABS） glass, the ABS glass can become glass-ceramics in the process of welding. ABS glass-ceramics have many excellent properties such as low thermal expansion cofficient, high chemical stablity, good resistance to acid and corrosion and good high-temperature resistance.The microstructure and morphology are researched by means of SEM, EDS, XRD and TEM. Study the influence of welding parameters on the microstructure and mechanical strength.The influence of B₂O₃/SiO₂ molar ratio（n） on crystallization behavior, softening temperature and high temperatue viscocity is very important. The project make four species of ABS glass interlayer（n=0.5, 1.5, 2.5, 3.5） by means of water quenching, they have good characteristics of amorphous and no obvious impurity.When using n=0.5 system ABS glass interlayer to connect Al₂O₃ ceramics with ZTA ceramics, the crystalline phase is granular Ca Al2Si2O8 crystal, there are many defects in the joint, the shearing strength is less than 10 MPa. When using n=1.5 system ABS glass interlayer, no reaction layer appears, the crystalline phases are Al4B2O9 whiskers and Al18B4O33 whiskers, the diameter of whiskers is about 0.5μm to 2μm, and the length of the whiskers ranges from 5μm to 12μm, the volume fraction of whiskers in the joint is about 50 percent. As the welding temperature increased, the shearing strength of the connecting joint increases at first and then decreases, the highest strength is about 42 MPa. After high temperature thermal cycle, the decline of strength is not obvious.When using n=2.5 system ABS glass interlayer to connect Al₂O₃ ceramics with ZTA ceramics, the thickness of reaction layer ranges from 5μm to 10μm, the diameter of whiskers is about 0.5μm to 2μm, and the length of the whiskers ranges from 10μm to 20μm, the volume fraction of whiskers in the joint increases to 80 percent. As the welding temperature increases, the shearing strength of the connecting joint increases at first and then decreases, the highest strength is about 45 MPa. When using n=3.5 system ABS glass interlayer, the volume fraction of whiskers in the joint decreases a little, the softening temperature of the middle layer increases, more defects such as cracks, porosity are found in the joint, so high temperature stability declines. When adding 5%wt Ti O₂ nucleation agent in the glass, it is disadvantageous to the strength of the connecting joint.The value of crystallization activation energy of ABS glass interlayer is calculated by Ozawa and K method. As the B₂O₃/Si O₂ molar ratio（n） increases, the crystallization activation energy decreases at first and then increases. When the molar ratio is 2.5, the energy reaches to minimum.