Residual stress and fracture strength of brazed joint of ceramic and titanium alloy with the aid of laser deposited functionally graded material layers

Abstract

To improve the strength of a ceramic (ZrC-SiC) and a titanium alloy (TC4) brazed joint, laser deposited functionally graded material layers (FGM layers) between ZrC-SiC and TC4 were designed to reduce the residual stress in the brazed joint. A simulation model of the brazed joint was created to investigate the mechanism of residual stress reduction due to FGM layers. The results show that the residual stress component in the normal direction of the brazing interface (normal stress) is tensile at the ZrC-SiC edges and the in-plane residual stress component on the brazing interface is compressive in the ZrC-SiC adjacent to the brazing seam. The adoption of the FGM layers significantly reduces both the normal residual stress and in-plane residual stress. During the shear test, the normal stress concentrates at the ZrC-SiC edges near the brazing seam. By applying fracture forces 645 N and 1365 N measured in shear experiments to the ZrC-SiC/TC4 joint model and ZrC-SiC/TC4-FGM joint model respectively, the local fracture stress in the normal direction is identified to be 648 MPa and 671 MPa from both models, respectively. Although the fracture force for both models are quite different due to the difference of residual stress produced by brazing, the identified local fracture stress is close each other. The predicted cracking initial position is around the corner of the ZrC-SiC close to the brazed zone which is the same as observed in experiments.