Recently, Ti-based refractory High Entropy Alloys (HEA), such as TiZrTaHfNb have been proposed to replace Ti6Al4V for biomedical applications due to the harmfulness of long term release of Al and V ions. With the aim of testing the possibility to produce ceramic-to-metal seals for these systems to be adopted in implantable medical devices, in this poster we present ZrO₂-Ag-HEA joints. To this end, the system reactivity, wettability of ZrO₂ by different Ag-based alloys at 1000°C and their interfacial layers were studied. Interpretation and discussion of systems reactivity were supported by thermodynamic calculations, according to the CALPHAD approach and the ad-hoc Ag-Ti-Zr-O thermodynamic database, implemented in this work. A good wettability was reached at 1000°C adding Ti to Ag: Ag-4Ti and Ag-8Ti reached contact angles of 81-85°. Ag-4Ti-2Zr showed the best wettability (77°) and the most complex interfacial microstructure. A continuous hcp-(Ti,O) layer promoted the wettability of Ag-4Ti and Ag-8Ti. In both cases, AgTi was the only intermetallic compound found in the bulk. Ag-4Ti-2Zr formed a thicker interfacial layer of hcp-(Ti,Zr,O)+bcc-(Ti,Zr) + a less compact Ag(Ti,Zr)₂ layer. Here, a low amount of Ag(Ti,Zr) and Ag(Ti,Zr)₂ was found in the Ag matrix.
Following the results from wettability tests, joints between ZrO₂ and a Ti_1.5ZrHf_0.5Ta_0.5Nb_0.5 HEA were produced at 1000 °C through a pure Ag brazing filler being the active elements, Ti and Zr, provided by diffusion from the HEA. The microstructural characterization showed defects and intermetallic-free interfaces with a first layer in contact with zirconia, mainly composed of Ag, Ti and Zr (HV ~ 600) followed by a plastic Ag-based area (HV ~ 250) extending until the HEA bulk. Further mechanical and electrochemical evaluations of the system are under way to demonstrate the possibility of using HEA-Ag-ZrO₂ joints for biomedical applications.