Brazing ZnS transparent ceramic to TA15 alloy using AgCuIn filler: Interfacial reactions and mechanical properties

ZnS transparent ceramic was successfully brazed to titanium alloy (TA15) using AgCuIn filler to produce optical windows for the first time. The microstructures of the joints were studied using scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The reaction layer adjacent to ZnS consists of CuInS₂ and Cu₂S at 700 °C for 10 min, then transforming into TiS, CuAlS₂, and nano-Cu₂S particles with increasing brazing temperature or holding time. Thermodynamic calculations indicate that the critical process behind these transformations is the diffusion of Ti and Al from TA15 to ZnS, and their involvement in interfacial reactions, resulting in the formation of a complex reaction layer that significantly affects mechanical properties. Notably, when the brazing process was conducted at 720 °C for 10 min, the joint exhibited a unique microstructure: ZnS/CuAlS₂+nano-Cu₂S particles + TiS/Cu(s, s) + Ag(s, s) + Cu₇In₃/TiS/Cu₂InTi + Ag(s, s)/CuTi/TA15. The optimized shear strength of the joint reached 45.2 MPa at room temperature and an impressive 33.1 MPa at 500 °C. This work realizes the reliable interface bonding between ZnS and metal, offering significant insights for assembling high-quality transparent ceramic/metal joints.