Effect of processing parameters on microstructure and mechanical properties of Al_2O_3/TC4 alloy joints

Al₂O₃ and TC4 alloy were brazed with Cu+B brazing filler at 890-970℃ for 10 min and at 930℃ 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 Ti₂(Cu, Al) existed, and the amounts of Ti₂(Cu, Al) and Ti+Ti₂(Cu, Al) increased.The size and distribution range of Ti+Ti₂(Cu, Al) also increased, which migrated to the TC4 alloy side.The hypereutectoid regions widened near the TC4 alloy.Below 950℃, the TiB whiskers were mainly dispersed on AlCu₂Ti in grain boundary of Ti₂Cu.While above 950℃, the AlCu₂Ti gradually disappeared, and TiB whiskers were mainly distributed on Ti₂Cu.When the holding time was 10 min and brazing temperature was 950℃, the maximal joint shear strength was 96 MPa.While the holding time was 20 min and brazing temperature was 930℃, and the maximal joint shear strength was 83 MPa.