Bonding of zirconia to super alloy with the active brazing technique

Zirconia stabilized with yttria was bonded to a Ni-based superalloy by acti ve brazing. An interlayer with the composition of the silver-copper eutecti c plus 1.75 wt.% titanium was used as brazing material. Various brazing hea ting cycles were performed using a furnace with graphite heating elements a nd under flowing argon. The microstructure of the bonded couples is related to the chemical reactions occurring during the brazing cycles, to the prop erties of the specific compounds formed and to the interdiffusion phenomena occurring across the interfaces. Critical feature for the success of the j oint is the nature of the interfaces that the brazing interlayer formed wit h the superalloy and the zirconia. At the interface with the superalloy adh esion is obtained under a relatively wide range of experimental conditions. On the contrary, at the interface with zirconia, a good wetting and adhesi on occurred only when a titanium oxide sublayer with a specific thickness f ormed. The best results were obtained with a maximum temperature between 87 0 and 900 degreesC, a soaking time of 10 min and a fast heating rate (10 de greesC/min). The optimal thickness of the TiOx sublayer was less than 1 mum . (C) 2000 Elsevier Science Ltd. All rights reserved.