Abstract
Strong metal-ceramic bonds require thermodynamic adhesion with the formation of new phases at the interface when the system is reactive, or without the formation of new phases when the system is non-reactive. The copper-alumina system can be reactive or non-reactive depending on the oxygen content in the atmosphere and/or in the copper. The non-reactive/reactive transition was determined and corresponded to an oxygen partial pressure of about 4.9 x 10-3 Torr. For solid-state bonding, in non-reactive conditions, the fracture strength of the bonds increased as the oxygen partial pressure tended towards this transition value. For reactive conditions, the growth of CuAlO2 induced a high interfacial fracture energy. For metal-alumina brazing, to enhance wetting, alumina was sprayed with copper powder in air and subsequently brazed using Ag-28 wt% Cu alloy. The surface-active effect of oxygen present in the Cu-Cu2O deposit favours the wetting of alumina by the AgCu brazing alloy, as well as adhesion, because of the segregation of silver at the metal-ceramic interface associated with the formation of Ag-O clusters.
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