Research On Brazing Technology Of Copper To SiO₂Ceramic

Ordinary electroceramics (alumina-silica based ceramic, referred to as SiO2ceramic), which possesses low thermal expansion coefficient and excellent thermalstability, is an essential insulating material in the development of electric industry. Theassembly of insulator and bushing, which are widely used in our life, requires joiningan ordinary electroceramic to metal in the insulator and bushing. During practicalapplications, the method to join metal to ceramics is just mechanical or adhesivebonding, which adversely affects the operation of the whole structure. Meanwhile,brazing is widely used to join ceramic and metal to achive metallurgical connection.Therefore, Ag-Cu-Ti filler alloy and nano-Al2O3strengthened Ag-Cu-Ti compositefiller were used to join the electroceramic to copper respectively in the present work,the formation mechanism and the effect of brazing parameters on interface structureand mechanical properties in the SiO2ceramic/Copper joints were investigated by themeans of SEM, EDAX, XRD and TEM. Furthermore, the value and distribution ofresidual stresses yielded in copper and SiO2ceramic joints with the two types of brazewere evaluated by finite element simulation method.Copper and SiO2ceramics were brazed with Ag-Cu-Ti filler metal, the typicalinterfacial microstructure of Copper/Ag-Cu-Ti/SiO2ceramic is as follows: SiO2ceramic/Ti5Si3+TiO/Ti2Cu+Ti3Cu3O/Ag(s,s)+Cu(s,s)/Copper. The results show that thebrazing parameters affect the thickness of interface reaction layer in the joints, whichwould increase when the brazing temperature was higher or holding time was longer.The highest shear strength was22MPa when brazed at850°C for5min usingAg-Cu-Ti with4.5wt.%Ti. The shear fracture shows that the fracture took place in twoplaces, which were ceramic side and the reaction layer.In order to adjust the thermal expansion coefficient of the interlayer and relievethe residual stress of the joints, nano-Al2O3strengthened Ag-Cu-Ti composite fillerwas used to braze Copper and SiO2ceramic. The typical interfacial microstructure ofCopper/composite filler/SiO2ceramics is as follows: SiO2ceramics/Ti5Si3+TiO/discontinuous Ti2Cu+Ti3Cu3O/Ag(s,s)+Ti2Cu＋nano-Al2O3＋Cu(s,s)/Cu. The resultsof TEM and SEM demonstrate that there are Ti2Cu and nano-Al2O3particlesdispersedly distributed in the Ag(s,s) and Cu(s,s). In addition, when the content of Al2O3pincreased from0to0.5wt.%, the thickness of interface reaction layer woulddecrease and the mount of Ti2Cu intermetallics would increase. The highest jointstrength (26MPa) can be obtained while the SiO2ceramic and Copper were brazed with(Ag72Cu28)96Ti4.5+0.3wt.%Al2O3at1193℃for10min, which is20%more than thatbrazed with Ag-Cu-Ti filler alloy alone.The results of numerical simulation of the SiO2ceramic/Copper joints brazed byAg-Cu-Ti filler show that there are higher residual stresses and residual tensile stress inthe ceramic adjacent to the reaction layer, and there occurred stress concentration in thejoints· edge. While residual stress distribution unchanged but both the stress area andstress peaks were reduced when composite brazing alloys were utilized.