Heterogeneous material joining of sapphire and TC4 alloy with a functionally graded interface

Abstract The natural high brittleness of sapphire leads to its poor machinability, which limits its application shape and size. The connection between sapphire and metal provides a new method to prepare large‐size sapphire components and complex structural parts. In this study, sapphire and TC4 alloy were joined by spark plasma sintering (SPS) diffusion technology with Al 2 O 3 ‐Ti as interlayer fillers. The effects of filler composition, sintering temperature, microstructure, and phase distribution on the strength of the joint were explored. The results showed that sapphire and TC4 could be well connected by SPS with Al 2 O 3 ‐Ti fillers. The microstructure of the joint showed no obvious defect or element enrichment. The optimized shear strength of sapphire/interlayer(Al 2 O 3 ‐Ti)/TC4 joint reached 121 MPa, and the fracture path mode was sapphire‐interlayer‐TC4, indicating the strong bonding between the heterogeneous materials. The sapphire/interlayer(Al 2 O 3 ‐Ti)/TC4 structure could relieve the residual stress caused by the difference in the thermal expansion coefficient in direct connection between sapphire and TC4.