EVOLUTION OF THE SECONDARY PHASE ALON IN ALN DURING ITS BONDING WITH CAO-DOPED TUNGSTEN

The reaction of AlON with CaO, which occurs during the direct bonding between AlN ceramics and CaO-doped doped tungsten, induces between 1400-degrees-C and 1650-degrees-C a fast demixing of oxynitride, proceeding with a reaction between the so-formed alumina and lime, producing calcium aluminates. Their compositions are those expected on the basis of the pseudo-binary phase diagrams of AlON (for the equivalent quantity of Al2O3 contained in the oxynitride) and Al2O3/CaO (for the nature of the aluminates). The aluminium nitride produced by the demixing remains after the reaction, except at the highest temperatures and CaO contents where it is dissolved by the calcium aluminate liquid phase to form a nitrogen glass. This overall behaviour is good for maintaining the properties of AlN ceramics after bonding with metal.