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 br azed joints were analysed by using the finite element method (FEM). Th e thermal and residual stresses which were induced mainly by the diffe rence in the thermal expansion coefficients between the brazed materia ls were successively calculated. The high tensile residual stress occu rred in the brazed joint interface, which has the potential to cause i nternal cracks in the brazed joints. In order to reduce the tensile re sidual stress in the brazed joint, the mechanical loading cycle was ad opted during the brazing thermal cycle. The calculation results reveal ed that the tensile residual stress in the brazed ceramics can be redu ced by the mechanical loading cycle and that the magnitude of the appl ied load and the temperature at which the mechanical loading cycle sta rted greatly influence the reduction amount of the tensile residual st ress. For a comparison of the simulation results, the residual stress in the brazed joints was measured by using the X-ray diffraction metho d. The results calculated by the FEM analysis showed a similar tendenc y 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 mechanica l loading cycle. The larger the applied load, the smaller was the tens ile residual stress occurring in the metal-to-ceramic brazed joint.