Metallization of Al2O3 ceramic by magnetron sputtering Ti/Mo bilayer thin films for robust brazing to Kovar alloy

Ti/Mo bilayer thin films were deposited onto Al₂O₃ ceramic by magnetron sputtering with a subsequent high temperature sintering to ensure the robust brazing of Al₂O₃ ceramic to Kovar (Fe–Ni–Co) alloy. The interface reaction process between Ti film and Al₂O₃ ceramic as well as the joining strength between metallized Al₂O₃ ceramic and Kovar alloy were investigated systematically using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and electronic universal testing machine. The results show that the active Ti film can react with Al₂O₃ ceramic to form Ti₃Al and TiO during high-temperature sintering process, in which the amount, size and morphology of TiO crucially depend on the sintering temperature. As the sintering temperature reaches 1200 °C, a plenty of spherical TiO nanoparticles with ~ 150 nm in diameter and metallic nature can be created across the Ti/Al₂O₃ interfaces, which can effectively act as ‘bridges’ to join Ti film to Al₂O₃ substrate firmly. Hence, the optimal joining strength of 69.6±3.1 MPa between metallized Al₂O₃ ceramic and Kovar alloy can be obtained, much better than those counterparts metallized at 900 °C and 1050 °C almost without the existence of observable TiO.