Effect of processing parameters on microstructure and mechanical properties of Al ₂O ₃/TC4 alloy joints

Al ₂O ₃ and TC4 alloy were brazed with Cu+B brazing filler at 890-970°C for 10 min and at 930°C for 0-30 min, respectively. The microstructure and mechanical properties of the resultant joints were investigated with SEM, EDS and shear testing machine. The results indicated that with the increasing of brazing temperature and holding time, the thickness of Ti4(Cu, Al) ₂O layer increased, next to which continuous and thick Ti ₂(Cu, Al) existed, and the amounts of Ti ₂(Cu, Al) and Ti+Ti ₂(Cu, Al) increased. The size and distribution range of Ti+Ti ₂(Cu, Al) also increased, which migrated to the TC4 alloy side. The hypereutectoid regions widened near the TC4 alloy. Below 950°C, the TiB whiskers were mainly dispersed on AlCu ₂Ti in grain boundary of Ti ₂Cu. While above 950°C, the AlCu ₂Ti gradually disappeared, and TiB whiskers were mainly distributed on Ti ₂Cu. When the holding time was 10 min and brazing temperature was 950°C, the maximal joint shear strength was 96 MPa. While the holding time was 20 min and brazing temperature was 930°C, and the maximal joint shear strength was 83 MPa.