An investigation on the vacuum brazed diamond film and copper using low-temperature Ag-Cu-Sn-Ti filler alloys: Interfacial microstructure and mechanical performance

The diamond microwave window is usually employed in the fusion reactor such as the international thermonuclear experimental reactor (ITER). To promote its fabrication, the diamond film needs to be brazed with copper rings. In this work, the diamond-copper combination was vacuum brazed using low-temperature AgCu-10Sn-1Ti filler alloys. The effects of brazing temperature and soaking time on the microstructure and mechanical performance of the joints were investigated. The Raman technique was used to probe the distribution of notorious residual stresses in the joints. Lastly, the intrinsic relationship between the microstructure, shear strength, and residual stresses of the joints was built. When brazed at low temperature or for short soaking duration (720 °C/5 min), some solidification defects and intermetallic clusters were formed, due to insufficient elemental diffusion and poor flowability of the interlayer. Increasing the brazing temperature or extending the soaking time would eliminate these defects, leading to microstructural homogeneity. The joint average shear strength optimized reached 256 MPa at 750 °C for 10 min. In such a case, the tensile stresses near the diamond/interlayer interface guided the fracture process. Otherwise, the metallurgical quality of interlayer would be responsible for the joint bond strength. The work performed furnished the way for the preparation of diamond microwave windows from technical and theoretical aspects.