Pre-oxidation of Ti and its diffusion bonding to K9 glass: microstructure and mechanism properties

In this work, a metal–glass joint between Ti and K9 glass was obtained by vacuum diffusion bonding after Ti was pre-oxidized at different temperatures to explore the effect of the pre-oxidation procedure on the properties of diffusion bonding joints. For the oxide layer, X-ray diffraction revealed that the oxide film consisted of TiO₂ and some low-valence Ti–O compounds such as Ti₆O, Ti₃O, TiO, etc. The x/y ratio of Ti_xO_y decreased as oxidation temperature increased. Scanning and transmission electron microscopy showed that the morphology of the oxide layer gradually changed from dense to loose and porous, and the oxidized particle size gradually increased and distributed in layers from inside to outside, with the increase in temperature. From the results of diffusion bonding at 700 °C for 2 h, good Ti-K9 joints without cracks and pores can be obtained when the pre-oxidation temperature attained 900 °C. A transition layer appeared at the Ti-K9 interface with the diffusion of elements Ti, Si, and O, etc. Shear strength tests showed that the structure of the oxide layer at different conditions can directly affect the strength of the joint between Ti and glass. The joint to Ti pre-oxidized at 900 °C exhibited the highest shear strength, producing an average failure strength of 20.6 ± 1.2 MPa. An appropriate amount of oxide layer can improve the quality of the Ti-K9 joint. The feasibility of diffusion bonding added to process versatility for the use of Ti-K9 joint on practical application.