Effect of Ti content on the metallization layer and copper / alumina brazed joint

The effects of Ti content on the evolution of metallization layer and microstructure and shear strength of copper / alumina brazed joint were investigated. A good bonded metallization layer in β-Sn matrix containing Ti₆Sn₅ phases was obtained on the surface of alumina at 900 °C for 30 min. Active Ti dissolved into liquid SAC and reacted with alumina to form TiO layer resulting in the spreading of melt. Therefore a more flat metallization layer covered on alumina as more Ti added into SAC. On the other hand, due to the violent reaction between element Ti and Sn, Ti₆Sn₅ precipitated in melt leading to the reduction of the fluidity of melt, and a discontinuous metallization layer was obtained for SAC-8%Ti. After metallization process, alumina was brazed to copper at 600 °C for 5 min. Typical microstructure of brazed joint was copper / Cu₃Sn layer / Cu₆Sn₅ layer / β-Sn layer containing Ti₆Sn₅ phases and Al₂O₃ particles / alumina. As the increase of Ti content, more Ti₆Sn₅ phases existed in brazing seam, which enhanced the shear strength of brazed joint, at 6%Ti, the highest value of 25 MPa was achieved. With the further increase of Ti content, the effective bonding area of copper / alumina brazed joint decreased and a corresponding lower shear strength was obtained.