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 ~ 150nm 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±3.1MPa 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.