Study On Interfacial Microstructure And Mechanical Properties Of Sapphire Epitaxial Connection With Ultrasonic Aided

As a kind of windows material, sapphire has been widely applied in aerospaceindustry because it has outstanding optical properties. Moreover, Sapphire is widelyused in light emitting diode substrate and semiconductor packaging with merits of highstrength and being resistant to corrosion, high temperature and so on. We will meetsome problems all the time when sapphire is joined by metal materials, such as hard toreaction, low wetting tendency and serious residual stress. In this study, brazing ofsapphire was implemented by using pure Al filler metal and AlCuMg filler metal. Wewill investigate the bonding mechanism of sapphire/solder interface with the action ofultrasonic and analyze joint microstructure and fracture characteristics. A suitableprocess of sapphire joints with high strength and low stress is researched.According to the study, the pure Al filler can react with sapphire on the wholesurface on ultrasonic aided at700℃, which generates Al2O3. Meanwhile, the fillermetals and sapphire are joined together by Al2O3which is the inter-layer of reactionproduct. As the ultrasound is applied longer, it appears a tendency that the Al2O3generated on the sapphire surface will be thicker and its form will transform fromamorphous to crystalline state.The sapphire joints is produced by ultrasonic brazing using pure Al. Shear fractureanalysis found that fracture occurs in the metal filler. It turn out that the metal fillerstrength is lower than both that of the combination Al2O3and sapphire and that of thecombination Al2O3and solder. Mechanical test results showed that with the extension ofultrasound duration, the joint shear strength does not change too much. The highestshear strength of the joints is49MPa. Solder itself is the weak link of welded joints.the AlCuMg filler can react with sapphire on the surface on ultrasonic aided at680℃, which generates MgAl2O4. As the ultrasound is applied longer, it appears atendency that the MgAl2O4generated on the sapphire surface will be thicker.Cracks exist in the base sapphire and at the metal/sapphire interfaces of thesapphire joints produced by ultrasonic brazing using pure Al with furnace cooling. Thehigh residual stress leads to cracks and other defects. Heat Treatment can remove cracksand other defects after brazing. The average and maximum shear strength is124.5MPaand127MPa by heat treatment. Compared with the joints by furnace cooling, the shear strength almost improves to100%.