Enhancing Interfacial Stability and Mechanical Strength of a CoSb₃-Based Thermoelectric Junction Using Ti-Based Alloy...

CoSb₃-based filled skutterudites (SKDs) are among the most promising materials for power generation. However, the poor interfacial stability and mechanical strength severely limit their practical application when joined with Cu electrodes. In this study, we propose multiphase Ti-based alloy barrier layers for CoSb₃-based thermoelectric junctions to prevent the continuous brittle TiCoSb phase formation. Following the principles of coefficient of thermal expansion matching, we designed three types of Ti_80-xNb_xCo₂₀ (x = 0, 5, and 10, at.%) barrier layers with the thin intermetallic compound (IMC) layers (<20 μm). Transmission electron microscopy analysis revealed that the interfacial microstructure of the Ti₇₅Nb₅Co₂₀/Ce-SKD junction comprises Ti₅Sb₃, Ti₅CoSb₃, TiCoSb, and TiSb₂ phases, as well as unreacted TiCo, Ti₂Co, and Ti(Nb)_ss phases, demonstrating a uniform staggered distribution state. After aging tests, the IMC thickness increased gradually from 7 to 12 μm, and the interfacial contact resistivity increased from 7.59 to 15.46 μΩ·cm². A Cu layer was chosen as a buffer during the brazing process to prevent the formation of cracks and holes. After aging for 360 h at 823 K, the shear strength of the brazed joints remained at ∼21 MPa. Our results demonstrate that the Cu/CuSnP/Cu/Ti₇₅Nb₅Co₂₀/Ce-SKD brazed joint exhibits excellent interfacial stability and satisfactory mechanical strength.