Releasing the residual stress of Al2O3/304 stainless steel joint by introducing BN into Ag‐Cu‐Ti filler metal

Abstract Owing to the native character of the coefficient of thermal expansion (CTE) mismatch between Al 2 O 3 and 304 stainless steel, obtaining high strength for Al 2 O 3 /304 stainless steel joints remains challenging. In this study, the residual stress of an Al 2 O 3 /304 stainless steel brazed joint was relieved using the Ag‐Cu‐Ti + boron nitride (BN) composite filler. The results indicated that the elements between the filler and base metals on both sides were mutually diffused. Moreover, reaction layers formed at the interface, connecting the Al 2 O 3 ceramic and 304 stainless steel. The microstructure of the joint was as follows: Al 2 O 3 /Cu 3 Ti 3 O + TiCu/Ag (s, s) + Cu (s, s) + TiN + TiB 2 + TiCu/Cu0.8Fe0.2Ti/TiFe 2 /Fe‐Cr/304 stainless steel. When the .1 wt% BN was added, the average strength of the joint reached 151 ± 10 MPa, 15% higher than the average strength of the joint only using Ag‐Cu‐Ti filler (131 ± 9 MPa). The improvement in the shear strength and reduction in the residual stress was attributed to the formation of TiN and TiB 2 , reducing the CTE difference and refining the microstructure.