A Study of the residual stress reduction method through the mechanical loading cycle in metal-to-ceramic brazed joints

The transient thermal and residual stresses in the metal-to-ceramic brazed joints were analysed by using the finite element method (FEM). The thermal and residual stresses which were induced mainly by the difference in the thermal expansion coefficients between the brazed materials were successively calculated. The high tensile residual stress occurred in the brazed joint interface, which has the potential to cause internal cracks in the brazed joints. In order to reduce the tensile residual stress in the brazed joint, the mechanical loading cycle was adopted during the brazing thermal cycle. The calculation results revealed that the tensile residual stress in the brazed ceramics can be reduced by the mechanical loading cycle and that the magnitude of the applied load and the temperature at which the mechanical loading cycle started greatly influence the reduction amount of the tensile residual stress. For a comparison of the simulation results, the residual stress in the brazed joints was measured by using the X-ray diffraction method. The results calculated by the FEM analysis showed a similar tendency to the results measured by the X-ray diffraction method. In the case of brazed joints with 0.1 mm thick filler metal, the residual stress in the ceramic part after the mechanical loading cycle showed a lower tensile stress compared to that of brazed joints without the mechanical loading cycle. The larger the applied load, the smaller was the tensile residual stress occurring in the metal-to-ceramic brazed joint.