Adhesion and reactivity in the copper-alumina system: influence of oxygen and silver

Strong metal-ceramic bonds require thermodynamic adhesion with the formatio n of new phases at the interface when the system is reactive, or without th e formation of new phases when the: system is non-reactive. The copper-alum ina system can be reactive or non-reactive depending on the oxygen content in the atmosphere and/or in the copper. The non-reactive/reactive transitio n was determined and corresponded to an oxygen partial pressure of about 4. 9 x 10(-3) Torr. For solid start bonding, in non-reactive conditions, the f racture strength of the bonds increased as the oxygen partial pressure tend ed towards this transition value. For reactive conditions, the growth of Cu AlO2 induced a high interfacial fracture energy. For metal-alumina brazing, to enhance welting, alumina was sprayed with copper powder in air and subs equently brazed using Ag-28 wt% Cu alloy. The surface-active effect of oxyg en present in the Cu-Cu2O deposit favours the wetting of alumina by the AgC u brazing alloy, as well as adhesion, because of the segregation of silver at the metal-ceramic interface associated with the formation of Ag-O cluste rs.