Joining of zirconia mechanically metallized with titanium

Abstract

Direct brazing is a well-known technique for joining ceramics either themselves or to metals, whereby the required costly active filler alloys are considered a handicap of this process. In this work the indirect brazing of zirconia to zirconia mechanically metallized with Ti was successfully achieved using conventional filler alloys. The mechanical metallization specially applied to oxide ceramics is a successfully technique that was patented by Forschungszentrum Juelich, Germany, and it has been the subject of applied researches in the last 10 years. This particular metallization is made at room temperature with low cost production and is environmentally safe. Partially stabilized zirconia with yttria was mechanically metallized with Ti and wetting conditions were evaluated using Ag-28Cu and Au-18Ni fillers. These conventional fillers dissolve part of the Ti-coating becoming on-site at brazing temperature an active filler alloy which reacts with the zirconium oxide to improve wetting on the ceramic surface. Better results were selected for brazing tests in a high-vacuum furnace (< 3×10-5 mbar). Helium gas leak detection was made at the ceramic/ceramic interface at room temperature; samples from reliable vacuum tight joints were examined by microestructural analysis and linescan technique by energy dispersive X-ray analysis in its cross-section. Microhardness profiles were made across the joint interface where zirconia undergone darkening after brazing process. Sound brazed joints were produced even when just one ceramic surface of the joint assemble was previously metallized, due to titanium diffusion from the metallized ceramic surface to the other ceramic side at the joint assemble.