Microstructure and mechanical properties of active brazed SiO2BN ceramic modified by electron-beam evaporated Ti

SiO2BN ceramic surface modified by electron-beam evaporated Ti was brazed to itself using an inactive AgCu eutectic alloy at 840 °C for 10 min. The effect of Ti content on the microstructure and mechanical properties of the joints was investigated by scanning and transmission electron microscopy and shear test. The results showed that the evaporated Ti layer dissolved into the liquid AgCu alloy rapidly and reacted with SiO2BN ceramic to form a TiNTiB2 fine-grain layer. AgCu eutectic structure in the center of the joint was gradually taken place by TiCu compounds with the increase of the Ti content. This microstructure evolution remarkably affected the shear strength of the joint. The highest shear strength of 39.2 MPa was obtained when the Ti content in the brazing alloy was 2.0 wt%. The joint strength was clearly improved when a soft Cu interlayer was inserted between two AgCu brazing foils. The effect of Cu-foil thickness on the microstructure and the shear strength of the joint was studied.