Improvement for Ti₃SiC₂/Cu joint brazed using composite fillers with abnormal expansion ceramic particulates

Reducing the residual stresses and improving the mechanical strength of large-scale ceramic/metal brazing joints is an important problem that must be solved for its practical engineering application. Using composite filler with solid-state phase transformation ceramic particulates, it is theoretically feasible to relieve the residual stress and improve the mechanical properties of ceramic/metal brazed joints. In this study, Cu mesh, Ag–28Cu–2Ti (wt.%), and yttria-stabilized zirconia (0.6 mol.% YSZ solid-state phase transformation ceramic particulates) composite power fillers were used in the brazing of Ti₃SiC₂ ceramic and pure copper. The microstructure of joints and YSZ particulates in the interface was investigated and confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). In addition, the effect of YSZ particulates content on the mechanical properties of joints was investigated and evaluated by the shear strength. The results show that the interfacial phases were mainly Ti₅Si₃, TiC, Ti_xCu, Ag (s, s), Cu (s, s), and YSZ particulates. Moreover, most of YSZ particulates undergo the solid-state phase transformation from tetragonal zirconia (t-ZrO₂) to monoclinic zirconia (m-ZrO₂) during the cooling process of brazing. The abnormal volume expansion of the solid-state phase transformation reduced the thermal mismatch between Ti₃SiC₂ ceramic and filler, thereby reducing the residual stress in the interface of joint. When using composite filler with 6 wt.% YSZ particulates, the shear strength of Ti₃SiC₂/Cu joint reached the maximum. The maximum average shear strength of the joints was 80.2 MPa, which was about 103.6% more than the joint without YSZ particulates.