Interfacial microstructure and properties of Al2O3/K-52 austenitic stainless-steel-brazed joints based on the Ni–45Ti filler alloy

Abstract

In this study, Al 2 O 3 workpieces and K-52 austenitic stainless steel (K-52 ASS) were brazed in vacuum by using the Ni 45Ti filler alloy. The typical interfacial microstructure of Al 2 O 3 /K-52 ASS and K-52 ASS/K-52 ASS joints brazed at 1350 °C for 30 min and the bonding properties of the brazed joints were investigated. The featured interfacial microstructure of Al 2 O 3 /K-52 ASS-brazed joints bonded at 1350 °C for 30 min comprised Al 2 O 3 , TiC layer, Cr 7 C 3 , γ-FeNi (s, s), and austenite matrix phases. The mechanism of Al 2 O 3 /K-52 ASS-brazed joint formation was discussed in detail. The free atoms in K-52 ASS and NiTi solder continuously diffused towards each other during brazing, and then, with the continued brazing reaction, they infinitely dissolved to form a solid solution without a phase interface due to severe mutual diffusion. A TiC reaction layer was formed adjacent to Al 2 O 3 at the joint interface. The joint brazed to K-52 ASS at 1300 °C for 30 min attained the maximum shear strength of 344 MPa, and the brittle fracture of the joint was transformed into a dimple-like ductile fracture at high temperature. The mechanical properties of the Al 2 O 3 /K-52 ASS joint were strongly related to the diffusion zone morphology. We brazed Al 2 O 3 workpieces and K-52 ASS by using the Ni 45Ti filler alloy under vacuum, the typical interfacial of Al 2 O 3 /K-52 ASS brazed-joint bonded at 1350 °C for 30 min comprised of Al 2 O 3 , TiC layer, Cr 7 C 3 , γ-FeNi (s, s), and austenite matrix phases. Strong interdiffusion occurred between K-52 ASS and the Ni 45Ti filler metal during brazing until they completely formed a solid solution without phase interfaces, which resulted in the formation of the TiC reaction layer adjacent to Al 2 O 3 along the liquid–solid interface. • Ni–45Ti (wt.%) filler metal was fabricated to braze Al 2 O 3 workpieces and K-52 ASS under vacuum. • The featured interfacial microstructure of Al 2 O 3 /K-52 ASS joints brazed at 1350 °C for 30 min were investigated. • The mechanism of Al 2 O 3 / K-52 ASS-brazed joint formation was thoroughly discussed. • The fracture morphology of the Al 2 O 3 /K-52 ASS and K-52 ASS/K-52 ASS brazed joints were analysed.