Calculation on residual stress of ZnO ceramic/copper brazed joints

Using thermal elastic plastic finite element method, the size and the distribution of residual stress in square ZnO ceramic/copper brazed joints were calculated. The results showed that residual stress existed in ZnO ceramic/copper brazed joints. The axial tensile stress of ZnO ceramic perpendicular to the brazed interface was the dominating factor that affects the performance of ZnO/Cu joints. The maximum axial tensile stress appeared at the edge of ZnO ceramic surface near the brazing interface. When the thickness of the filler metal was 0.3 mm, the maximum value of tensile stress (69.75 MPa) appeared at the edge of ZnO ceramic surface, 0.6 mm away from the ZnO/brazing interface. Comparison and calculation of brazing filler with different thicknesses showed that suitable filler metal thickness could reduce the residual stress of ZnO/Cu joints. Optimal thickness of the filler metal was 0.1 mm, while the peak tensile stress at ZnO ceramic side got a minimum value of 30.82 MPa. In addition, the influence of porosity defect at filler metal layers on residual stress of ZnO/Cu joints was studied using a single defect model. The simulation results showed that the maximum residual tensile stresses of ZnO/Cu joints were 95.5 and 107.2 MPa, respectively, when porosity defect existed in ZnO/In and Cu/In interface. Besides, the presence of porosity defect at filler metal layers caused a dramatic rise of tensile stress peak value. © 2015, Editorial Office of Chinese Journal of Rare Metals. All right reserved.